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The article may be interesting for developers who use or plan to use OpenC++ library (OpenCxx). The author tells about his experience of improving OpenC++ library and modifying the library for solving special tasks.
One may often here in forums that there are a lot of C++ syntax analyzers ("parsers"), and many of them are free. Or that one may take YACC, for example, and realize his own analyzer easily. Don't believe, it is not so easy. One may understand it especially if one remembers that it is even not half a task to parse syntax. It is necessary to realize structures for storing the program tree and semantic tables containing information about different objects and their scopes. It is especially important while developing specialized applications related to the processing and static analysis of C++ code. It is necessary for their realization to save the whole program tree what may be provided by few libraries. One of them is open library OpenC++ (OpenCxx) about which we'll speak in this article.
We'd like to help developers in mastering OpenC++ library and share our experience of modernization and improvement of some defects. The article is a compilation of pieces of advice, each of which is devoted to correction of some defect or realization of improvement.
The article is based on recollections about changes that were carried out in VivaCore library based on OpenC++. Of course, only a small part of these changes is discussed here. It is a difficult task to remember and describe them all. And, for example, description of addition of C language support into OpenC++ library will take too much place. But you can always refer to original texts of VivaCore library and get a lot of interesting information.
It remains to say that OpenC++ library is unfortunately out-of-date now and needs serious improvement for supporting the modern C++ language standard. That's why if you are going to realize a modern compiler for example, you'd better pay your attention to GCC or to commercial libraries. But OpenC++ still remains a good and convenient tool for many developers in the sphere of systems of specialized processing and modification of program code. With the use of OpenC++ many interesting solutions are developed, for example, execution environment OpenTS for T++ programming language (development of Program systems Institution RAS), static code analyzer Viva64 or Synopsis tool for preparing documentation on the original code.
The purpose of the article is to show by examples how one can modify and improve OpenC++ library code. The article describes 15 library modifications related to error correction or addition of new functionality. Each of them not only allows to make OpenC++ library better but also gives an opportunity to study its work principles deeper. Let's get acquainted with them.
While developing a code analyzer for a specific development environment, you are likely to come across with its specific language constructions. These constructions are often guidance for a concrete compiler and may not be of interest for you. But such constructions cannot be processed by OpenC++ library as they are not a part of C++ language. In this case one of the simplest ways to ignore them is to add them into rw_table table with ignore key. For example:
static rw_table table[] = {
...
{ "__ptr32", Ignore},
{ "__ptr64", Ignore},
{ "__unaligned", Ignore},
...
};While adding you should keep in mind that words in rw_table table should be arranged in alphabetic order. Be careful.
If you want to add a keyword which should be processed, you need to create a new lexeme ("token"). Let's look at the example of adding a new keyword "__w64". At first create an identifier of the new lexeme (see token-name.h file), for example in this way:
enum {
Identifier = 258,
Constant = 262,
...
W64 = 346, // New token name
...
};Modernize the table "table" in lex.cc file:
static rw_table table[] = {
...
{ "__w64", W64 },
...
};The next step is to create a class for the new lexeme, which we'll call LeafW64.
namespace Opencxx
{
class LeafW64 : public LeafReserved {
public:
LeafW64(Token& t) : LeafReserved(t) {}
LeafW64(char* str, ptrdiff_t len) :
LeafReserved(str, len) {}
ptrdiff_t What() { return W64; }
};
}To create an object we'll need to modify optIntegralTypeOrClassSpec() function:
...
case UNSIGNED :
flag = 'U';
kw = new (GC) LeafUNSIGNED(tk);
break;
case W64 : // NEW!
flag = 'W';
kw = new (GC) LeafW64(tk);
break;
...Pay attention that as far as we've decided to refer "__w64" to data types, we'll need the 'W' symbol for coding this type. You may learn more about type coding mechanism in Encoding.cc file.
Introducing a new type we must remember that we need to modernize such functions as Parser::isTypeSpecifier() for example.
And the last important point is modification of Encoding::MakePtree function:
Ptree* Encoding::MakePtree(unsigned char*& encoded, Ptree* decl)
{
...
case 'W' :
typespec = PtreeUtil::Snoc(typespec, w64_t);
break;
...
}Of course, it is only an example, and adding other lexemes may take much more efforts. A good way to add a new lexeme correctly is to take one close to it in sense and then find and examine all the places in OpenC++ library where it is used.
We have already examined the way of skipping single keywords which are senseless for our program but impede code parsing. Unfortunately, sometimes it is even more difficult. Let's take for demonstration such constructions as __pragma and __noop which you may see in header files of VisualC++:
__forceinline DWORD HEAP_MAKE_TAG_FLAGS (
DWORD TagBase, DWORD Tag )
{
__pragma(warning(push)) __pragma(warning(disable : 4548)) do
{__noop(TagBase);} while((0,0) __pragma(warning(pop)) );
return ((DWORD)((TagBase) + ((Tag) << 18)));
}You may look for description of __pragma and __noop constructions in MSDN. The next points are important for our program: a) they are not of interest for us; b) they have some parameters; c) they impede code analysis.
Let's add new lexemes at first, as it was told before, but now let's use InitializeOtherKeywords() function for this purpose:
static void InitializeOtherKeywords(bool recognizeOccExtensions)
{
...
verify(Lex::RecordKeyword("__pragma", MSPRAGMA));
verify(Lex::RecordKeyword("__noop", MS__NOOP));
...
}Solution consists in modifying Lex::ReadToken function so that when we come across with DECLSPEC or MSPRAGMA lexeme we skip it. And then we skip all the lexemes related to __pragma and __noop parameters. For skipping all the unnecessary lexemes we use SkipDeclspecToken() function as it is shown further.
ptrdiff_t Lex::ReadToken(char*& ptr, ptrdiff_t& len)
{
...
else if(t == DECLSPEC){
SkipDeclspecToken();
continue;
}
else if(t == MSPRAGMA) { // NEW
SkipDeclspecToken();
continue;
}
else if(t == MS__NOOP) { //NEW
SkipDeclspecToken();
continue;
}
...
}In tasks of analysis of original code a large amount of functionality is related to creation of error messages and also to navigation on original files. What is inconvenient is that file names returned by such functions as Program::LineNumber() may be presented in different ways. Here are some examples:
C:\\Program Files\\MSVS 8\\VC\\atlmfc\\include\\afx.h
.\\drawing.cpp
c:\\src\\wxwindows-2.4.2\\samples\\drawing\\wx/defs.h
Boost\\boost-1_33_1\\boost/variant/recursive_variant.hpp
..\\FieldEdit2\\Src\\amsEdit.cpp
..\\..\\..\\src\\base\\ftbase.cThe way may be full or relative. Different delimiters may be used. All this makes the use of such ways inconvenient for processing or for output in information messages. That's why we offer realization of FixFileName() function bringing paths to uniform full way. An auxiliary function GetInputFileDirectory() is used to return the path to the catalogue where the processed file is situated.
const string &GetInputFileDirectory() {
static string oldInputFileName;
static string fileDirectory;
string dir;
VivaConfiguration &cfg = VivaConfiguration::Instance();
string inputFileName;
cfg.GetInputFileName(inputFileName);
if (oldInputFileName == inputFileName)
return fileDirectory;
oldInputFileName = inputFileName;
filesystem::path inputFileNamePath(inputFileName,
filesystem::native);
fileDirectory = inputFileNamePath.branch_path().string();
if (fileDirectory.empty()) {
TCHAR curDir[MAX_PATH];
if (GetCurrentDirectory(MAX_PATH, curDir) != 0) {
fileDirectory = curDir;
} else {
assert(false);
}
}
algorithm::replace_all(fileDirectory, "/", "\\");
to_lower(fileDirectory);
return fileDirectory;
}
typedef map<string, string> StrStrMap;
typedef StrStrMap::iterator StrStrMapIt;
void FixFileName(string &fileName) {
static StrStrMap FileNamesMap;
StrStrMapIt it = FileNamesMap.find(fileName);
if (it != FileNamesMap.end()) {
fileName = it->second;
return;
}
string oldFileName = fileName;
algorithm::replace_all(fileName, "/", "\\");
algorithm::replace_all(fileName, "\\\\", "\\");
filesystem::path tmpPath(fileName, filesystem::native);
fileName = tmpPath.string();
algorithm::replace_all(fileName, "/", "\\");
to_lower(fileName);
if (fileName.length() < 2) {
assert(false);
FileNamesMap.insert(make_pair(oldFileName, fileName));
return;
}
if (fileName[0] == '.' && fileName[1] != '.') {
const string &dir = GetInputFileDirectory();
if (!dir.empty())
fileName.replace(0, 1, dir);
FileNamesMap.insert(make_pair(oldFileName, fileName));
return;
}
if (isalpha(fileName[0]) && fileName[1] == ':' ) {
FileNamesMap.insert(make_pair(oldFileName, fileName));
return;
}
const string &dir = GetInputFileDirectory();
if (dir.empty())
fileName.insert(0, ".\\");
else {
fileName.insert(0, "\\");
fileName.insert(0, dir);
}
FileNamesMap.insert(make_pair(oldFileName, fileName));
}The function of getting a value of a numerical literal may be useful in systems of building documentation on the code. For example, with its help one may see that the argument of "void foo(a = 99)" function is 99 and use this for some purpose.
GetLiteralType() function that we offer allows to get the literal type and its value if it is integer. GetLiteralType() function is created for getting information needed most often and doesn't support rarely used record types. But if you need to support UCNs for example or get values of double type, you may expand functionality of the functions given below by yourself.
", 5) == 0) { retValue = 0; ; } ; }
IsHexLiteral( *from, size_t len)
{
(len < 3);
(from[0] != '0');
(from[1] != 'x' && from[1] != 'X');;
}
SimpleType GetTypeBySufix( *from, size_t len)
{
assert(from != NULL);
(len == 0)
ST_INT;
assert(!isdigit(*from));
suffix_8 = ;
suffix_16 = ;
suffix_32 = ;
suffix_64 = ;
suffix_i = ;
suffix_l = ;
suffix_u = ;
(len != 0)
{
--len;
c = *from++;
(c)
{
'8': suffix_8 = ; ;
'1': (len == 0 || *from++ != '6')
{
assert();
ST_UNKNOWN;
}
--len;
suffix_16 = ; ;
'3': (len == 0 || *from++ != '2')
{
assert();
ST_UNKNOWN;
}
--len;
suffix_32 = ; ;
'6': (len == 0 || *from++ != '4')
{
assert();
ST_UNKNOWN;
}
--len;
suffix_64 = ; ;
'I': 'i': suffix_i = ; ;
'U': 'u': suffix_u = ; ;
'L': 'l': suffix_l = ; ; : assert();
ST_UNKNOWN;
}
}
assert(suffix_8 + suffix_16 + suffix_32 + suffix_64 <= 1);
(suffix_8 || suffix_16)
ST_LESS_INT;
(suffix_32)
{
(suffix_u)
ST_UINT;
ST_INT;
}
(suffix_64)
{
(suffix_u)
ST_UINT64;
ST_INT64;
}
(suffix_l)
{
(suffix_u)
ST_ULONG;
ST_LONG;
}
(suffix_u)
ST_UINT;
assert(suffix_i);
ST_INT;
}
SimpleType GetHexLiteral( *from, size_t len, &retValue)
{
assert(len >= 3);
*p = from + 2;
(!GetHex(p, len, retValue))
{
ST_UNKNOWN;
}
ptrdiff_t newLen = len - (p - from);
assert(newLen >= 0 && newLen < <ptrdiff_t>(len));
GetTypeBySufix(p, newLen);
}
IsOctLiteral( *from, size_t len)
{
(len < 2);
(from[0] != '0');;
}
SimpleType GetOctLiteral( *from, size_t len,&retValue)
{
assert(len >= 2);
*p = from + 1; (
!GetOct(p, len, retValue))
{
ST_UNKNOWN;
}
ptrdiff_t newLen = len - (p - from); assert(newLen >= 0 && newLen
< <ptrdiff_t>(len));
GetTypeBySufix(p, newLen);
}
SimpleType GetDecLiteral( *from, size_t len, &retValue)
{
assert(len >= 1);
*limit = from + len;
n = 0;
(from < limit)
{
c = *from;
(c < '0' || c > '9');
from++;
n = n * 10 + (c - '0');
}
ptrdiff_t newLen = limit - from; (newLen == <ptrdiff_t>(len))
ST_UNKNOWN;
retValue = n;
assert(newLen >= 0 && newLen < <ptrdiff_t>(len));
GetTypeBySufix(from, newLen);
}
SimpleType GetLiteralType( *from, size_t len, &retValue)
{
(from == NULL || len == 0)
ST_UNKNOWN;
retValue = 1;
(from == NULL || len == 0)
ST_UNKNOWN;
(GetCharLiteral(from, len, retValue))
ST_LESS_INT;
(GetStringLiteral(from, len))
ST_POINTER;
(GetBoolLiteral(from, len, retValue))
ST_LESS_INT;
(IsRealLiteral(from, len))
GetRealLiteral(from, len);
(IsHexLiteral(from, len))
GetHexLiteral(from, len, retValue);
(IsOctLiteral(from, len))
GetOctLiteral(from, len, retValue);
GetDecLiteral(from, len, retValue);
}
unsigned __int64 GetHexValue(unsigned char c) {
if (c >= '0' && c <= '9')
return c - '0';
if (c >= 'a' && c <= 'f')
return c - 'a' + 0x0a;
if (c >= 'A' && c <= 'F')
return c - 'A' + 0x0a;
assert(false);
return 0;
}
bool GetHex(const char *&from, size_t len,
unsigned __int64 &retValue) {
unsigned __int64 c, n = 0, overflow = 0;
int digits_found = 0;
const char *limit = from + len;
while (from < limit)
{
c = *from;
if (!isxdigit(c))
break;
from++;
overflow |= n ^ (n << 4 >> 4);
n = (n << 4) + GetHexValue(c);
digits_found = 1;
}
if (!digits_found)
return false;
if (overflow) {
assert(false);
}
retValue = n;
return true;
}
bool GetOct(const char *&from, size_t len,
unsigned __int64 &retValue) {
unsigned __int64 c, n = 0;
bool overflow = false;
const char *limit = from + len;
while (from < limit)
{
c = *from;
if (c < '0' || c > '7')
break;
from++;
overflow |= static_cast<bool>(n ^ (n << 3 >> 3));
n = (n << 3) + c - '0';
}
retValue = n;
return true;
}
#define HOST_CHARSET_ASCII
bool GetEscape(const char *from, size_t len,
unsigned __int64 &retValue) {
/* Values of \a \b \e \f \n \r \t \v respectively. */
// HOST_CHARSET_ASCII
static const char charconsts[] =
{ 7, 8, 27, 12, 10, 13, 9, 11 };
// HOST_CHARSET_EBCDIC
//static const uchar charconsts[] =
{ 47, 22, 39, 12, 21, 13, 5, 11 };
unsigned char c;
c = from[0];
switch (c)
{
/* UCNs, hex escapes, and octal escapes
are processed separately. */
case 'u': case 'U':
// convert_ucn - not supported. Return: 65535.
retValue = 0xFFFFui64;
return true;
case 'x': {
const char *p = from + 1;
return GetHex(p, len, retValue);
}
case '0': case '1': case '2': case '3':
case '4': case '5': case '6': case '7': {
const char *p = from + 1;
return GetOct(p, len, retValue);
}
case '\\': case '\'': case '"': case '?':
break;
case 'a': c = charconsts[0]; break;
case 'b': c = charconsts[1]; break;
case 'f': c = charconsts[3]; break;
case 'n': c = charconsts[4]; break;
case 'r': c = charconsts[5]; break;
case 't': c = charconsts[6]; break;
case 'v': c = charconsts[7]; break;
case 'e': case 'E': c = charconsts[2]; break;
default:
assert(false);
return false;
}
retValue = c;
return true;
}
//'A', '\t', L'A', '\xFE'
static bool GetCharLiteral(const char *from,
size_t len,
unsigned __int64 &retValue) {
if (len >= 3) {
if (from[0] == '\'' && from[len - 1] == '\'') {
unsigned char c = from[1];
if (c == '\\') {
verify(GetEscape(from + 2, len - 3, retValue));
} else {
retValue = c;
}
return true;
}
}
if (len >= 4) {
if (from[0] == 'L' &&
from[1] == '\'' &&
from[len - 1] == '\'') {
unsigned char c = from[2];
if (c == '\\') {
verify(GetEscape(from + 3, len - 4, retValue));
} else {
retValue = c;
}
return true;
}
}
return false;
}
// "string"
static bool GetStringLiteral(const char *from, size_t len) {
if (len >= 2) {
if (from[0] == '"' && from[len - 1] == '"')
return true;
}
if (len >= 3) {
if (from[0] == 'L' &&
from[1] == '"' &&
from[len - 1] == '"')
return true;
}
return false;
}
bool IsRealLiteral(const char *from, size_t len) {
if (len < 2)
return false;
bool isReal = false;
bool digitFound = false;
for (size_t i = 0; i != len; ++i) {
unsigned char c = from[i];
switch(c) {
case 'x': return false;
case 'X': return false;
case 'f': isReal = true; break;
case 'F': isReal = true; break;
case '.': isReal = true; break;
case 'e': isReal = true; break;
case 'E': isReal = true; break;
case 'l': break;
case '-': break;
case '+': break;
case 'L': break;
default:
if (!isdigit(c))
return false;
digitFound = true;
}
}
return isReal && digitFound;
}
SimpleType GetRealLiteral(const char *from, size_t len) {
assert(len > 1);
unsigned char rc1 = from[len - 1];
if (is_digit(rc1) || rc1 == '.' ||
rc1 == 'l' || rc1 == 'L' ||
rc1 == 'e' || rc1 == 'E')
return ST_DOUBLE;
if (rc1 == 'f' || rc1 == 'F')
return ST_FLOAT;
assert(false);
return ST_UNKNOWN;
}
bool GetBoolLiteral(const char *from, size_t len,
unsigned __int64 &retValue) {
if (len == 4 && strncmp(from, "true", 4) == 0) {
retValue = 1;
return true;
}
if (len == 5 && strncmp(from, "false", 5) == 0) {
retValue = 0;
return true;
}
return false;
}
bool IsHexLiteral(const char *from, size_t len) {
if (len < 3)
return false;
if (from[0] != '0')
return false;
if (from[1] != 'x' && from[1] != 'X')
return false;
return true;
}
SimpleType GetTypeBySufix(const char *from, size_t len) {
assert(from != NULL);
if (len == 0)
return ST_INT;
assert(!isdigit(*from));
bool suffix_8 = false;
bool suffix_16 = false;
bool suffix_32 = false;
bool suffix_64 = false;
bool suffix_i = false;
bool suffix_l = false;
bool suffix_u = false;
while (len != 0) {
--len;
const char c = *from++;
switch(c) {
case '8': suffix_8 = true; break;
case '1':
if (len == 0 || *from++ != '6') {
assert(false);
return ST_UNKNOWN;
}
--len;
suffix_16 = true;
break;
case '3':
if (len == 0 || *from++ != '2') {
assert(false);
return ST_UNKNOWN;
}
--len;
suffix_32 = true;
break;
case '6':
if (len == 0 || *from++ != '4') {
assert(false);
return ST_UNKNOWN;
}
--len;
suffix_64 = true;
break;
case 'I':
case 'i': suffix_i = true; break;
case 'U':
case 'u': suffix_u = true; break;
case 'L':
case 'l': suffix_l = true; break;
default:
assert(false);
return ST_UNKNOWN;
}
}
assert(suffix_8 + suffix_16 + suffix_32 + suffix_64 <= 1);
if (suffix_8 || suffix_16)
return ST_LESS_INT;
if (suffix_32) {
if (suffix_u)
return ST_UINT;
else
return ST_INT;
}
if (suffix_64) {
if (suffix_u)
return ST_UINT64;
else
return ST_INT64;
}
if (suffix_l) {
if (suffix_u)
return ST_ULONG;
else
return ST_LONG;
}
if (suffix_u)
return ST_UINT;
assert(suffix_i);
return ST_INT;
}
SimpleType GetHexLiteral(const char *from, size_t len,
unsigned __int64 &retValue) {
assert(len >= 3);
const char *p = from + 2;
if (!GetHex(p, len, retValue)) {
return ST_UNKNOWN;
}
ptrdiff_t newLen = len - (p - from);
assert(newLen >= 0 && newLen < static_cast<ptrdiff_t>(len));
return GetTypeBySufix(p, newLen);
}
bool IsOctLiteral(const char *from, size_t len) {
if (len < 2)
return false;
if (from[0] != '0')
return false;
return true;
}
SimpleType GetOctLiteral(const char *from, size_t len,
unsigned __int64 &retValue) {
assert(len >= 2);
const char *p = from + 1;
if (!GetOct(p, len, retValue)) {
return ST_UNKNOWN;
}
ptrdiff_t newLen = len - (p - from);
assert(newLen >= 0 && newLen < static_cast<ptrdiff_t>(len));
return GetTypeBySufix(p, newLen);
}
SimpleType GetDecLiteral(const char *from, size_t len,
unsigned __int64 &retValue) {
assert(len >= 1);
const char *limit = from + len;
unsigned __int64 n = 0;
while (from < limit) {
const char c = *from;
if (c < '0' || c > '9')
break;
from++;
n = n * 10 + (c - '0');
}
ptrdiff_t newLen = limit - from;
if (newLen == static_cast<ptrdiff_t>(len))
return ST_UNKNOWN;
retValue = n;
assert(newLen >= 0 && newLen < static_cast<ptrdiff_t>(len));
return GetTypeBySufix(from, newLen);
}
SimpleType GetLiteralType(const char *from, size_t len,
unsigned __int64 &retValue) {
if (from == NULL || len == 0)
return ST_UNKNOWN;
retValue = 1;
if (from == NULL || len == 0)
return ST_UNKNOWN;
if (GetCharLiteral(from, len, retValue))
return ST_LESS_INT;
if (GetStringLiteral(from, len))
return ST_POINTER;
if (GetBoolLiteral(from, len, retValue))
return ST_LESS_INT;
if (IsRealLiteral(from, len))
return GetRealLiteral(from, len);
if (IsHexLiteral(from, len))
return GetHexLiteral(from, len, retValue);
if (IsOctLiteral(from, len))
return GetOctLiteral(from, len, retValue);
return GetDecLiteral(from, len, retValue);
}We offer you to modify Lex::ReadStrConst() function as it is shown further. This will allow to correct two errors related to processing of separated string literals. The first error occurs while processing strings of the following kind:
const char *name = "Viva\
Core";The second:
const wchar_t *str = L"begin"L"end".The corrected function variant:
bool Lex::ReadStrConst(size_t top, bool isWcharStr)
{
char c;
for(;;){
c = file->Get();
if(c == '\\'){
c = file->Get();
// Support: "\"
if (c == '\r') {
c = file->Get();
if (c != '\n')
return false;
} else if(c == '\0')
return false;
}
else if(c == '"</str>'){
size_t pos = file->GetCurPos() + 1;
ptrdiff_t nline = 0;
do{
c = file->Get();
if(c == '\n')
++nline;
} while(is_blank(c) || c == '\n');
if (isWcharStr && c == 'L') {
//Support: L"123" L"456" L "789".
c = file->Get();
if(c == '"')
/* line_number += nline; */ ;
else{
file->Unget();
return false;
}
} else {
if(c == '"')
/* line_number += nline; */ ;
else{
token_len = ptrdiff_t(pos - top);
file->Rewind(pos);
return true;
}
}
}
else if(c == '\n' || c == '\0')
return false;
}
}There is an error in OpenC++ related to the processing of some expressions which are wrongly taken for templates. For example, in a string "bool r = a < 1 || b > (int) 2;" "a" variable will be taken for a template name and then a lot of troubles with syntactical analysis will follow... Full correction of this error requires great changes and is not realized by now. We offer you a temporary solution excluding the major part of errors. Further the functions are given which may be added or modified.
bool VivaParser::MaybeTypeNameOrClassTemplate(Token &token) {
if (m_env == NULL) {
return true;
}
const char *ptr = token.GetPtr();
ptrdiff_t len = token.GetLen();
Bind *bind;
bool isType = m_env->LookupType(ptr, len, bind);
return isType;
}
static bool isOperatorInTemplateArg(ptrdiff_t t) {
return t == AssignOp || t == EqualOp || t == LogOrOp ||
t == LogAndOp || t == IncOp || t == RelOp;
}
/*
template.args : '<' any* '>'
template.args must be followed by '(' or '::'
*/
bool Parser::isTemplateArgs()
{
ptrdiff_t i = 0;
ptrdiff_t t = lex->LookAhead(i++);
if(t == '<'){
ptrdiff_t n = 1;
while(n > 0){
ptrdiff_t u = lex->LookAhead(i++);
/*
TODO. :(
Fixing: bool r = a < 1 || b > (int) 2;
We'll correct not all the cases but it will be better
anyway.
Editing method. If an identifier is found near the
operator, it is
obviously not a template because only a type or a constant
expression may stay inside the brackets.
An example which doesn't work anyway:
r = a < fooi() || 1 > (int) b;
Unfortunately, the following expression is processed
incorrectly now,
but such cases are fewer than corrected ones.
template <int z>
unsigned TFoo(unsigned a) {
return a + z;
}
enum EEnum { EE1, EE2 };
b = TFoo < EE1 && EE2 > (2);
*/
ptrdiff_t next = lex->LookAhead(i);
if (u == Identifier &&
isOperatorInTemplateArg(next))
return false;
if (isOperatorInTemplateArg(u) &&
next == Identifier)
return false;
if(u == '<')
++n;
else if(u == '>')
--n;
else if(u == '('){
ptrdiff_t m = 1;
while(m > 0){
ptrdiff_t v = lex->LookAhead(i++);
if(v == '(')
++m;
else if(v == ')')
--m;
else if(v == '\0' || v == ';' || v == '}')
return false;
}
}
else if(u == '\0' || u == ';' || u == '}')
return false;
}
t = lex->LookAhead(i);
return bool(t == Scope || t == '(');
}
return false;
}Unfortunately, the error correction mechanism in OpenC++ sometimes causes program crash. Problem places in OpenC++ are the code similar to this:
if(!rDefinition(def)){
if(!SyntaxError())
return false;
SkipTo('}');
lex->GetToken(cp); // WARNING: crash in the same case.
body = PtreeUtil::List(new Leaf(op), 0, new Leaf(cp));
return true;
}One should pay attention to those places where the processing of errors occurs and correct them the way shown by the example of Parser::rLinkageBody() and Parser::SyntaxError() functions. The general sense of the corrections is that after an error occurs, at first presence of the next lexeme should be checked with the use of CanLookAhead() function instead of immediate extraction of it by using GetToken,().
bool Parser::rLinkageBody(Ptree*& body)
{
Token op, cp;
Ptree* def;
if(lex->GetToken(op) != '{')
return false;
body = 0;
while(lex->LookAhead(0) != '}'){
if(!rDefinition(def)){
if(!SyntaxError())
return false; // too many errors
if (lex->CanLookAhead(1)) {
SkipTo('}');
lex->GetToken(cp);
if (!lex->CanLookAhead(0))
return false;
} else {
return false;
}
body =
PtreeUtil::List(new (GC) Leaf(op), 0,
new (GC) Leaf(cp));
return true; // error recovery
}
body = PtreeUtil::Snoc(body, def);
}
lex->GetToken(cp);
body = new (GC)
PtreeBrace(new (GC) Leaf(op), body, new (GC) Leaf(cp));
return true;
}
bool Parser::SyntaxError()
{
syntaxErrors_ = true;
Token t, t2;
if (lex->CanLookAhead(0)) {
lex->LookAhead(0, t);
} else {
lex->LookAhead(-1, t);
}
if (lex->CanLookAhead(1)) {
lex->LookAhead(1, t2);
} else {
t2 = t;
}
SourceLocation location(GetSourceLocation(*this, t.ptr));
string token(t2.ptr, t2.len);
errorLog_.Report(ParseErrorMsg(location, token));
return true;
}Without going into details we offer you to replace rTemplateDecl2() function with the given variant. This will exclude some errors while working with template classes.
bool Parser::rTemplateDecl2(Ptree*& decl,
TemplateDeclKind &kind)
{
Token tk;
Ptree *args = 0;
if(lex->GetToken(tk) != TEMPLATE)
return false;
if(lex->LookAhead(0) != '<') {
if (lex->LookAhead(0) == CLASS) {
// template instantiation
decl = 0;
kind = tdk_instantiation;
return true; // ignore TEMPLATE
}
decl = new (GC)
PtreeTemplateDecl(new (GC) LeafReserved(tk));
} else {
decl = new (GC)
PtreeTemplateDecl(new (GC) LeafReserved(tk));
if(lex->GetToken(tk) != '<')
return false;
decl = PtreeUtil::Snoc(decl, new (GC) Leaf(tk));
if(!rTempArgList(args))
return false;
if(lex->GetToken(tk) != '>')
return false;
}
decl =
PtreeUtil::Nconc(decl,
PtreeUtil::List(args, new (GC) Leaf(tk)));
// ignore nested TEMPLATE
while (lex->LookAhead(0) == TEMPLATE) {
lex->GetToken(tk);
if(lex->LookAhead(0) != '<')
break;
lex->GetToken(tk);
if(!rTempArgList(args))
return false;
if(lex->GetToken(tk) != '>')
return false;
}
if (args == 0)
// template < > declaration
kind = tdk_specialization;
else
// template < ... > declaration
kind = tdk_decl;
return true;
}In some cases it is necessary to know in what places of the program text there is the code from which a particular Ptree object was built.
The function given below returns the address of the beginning and the end of memory space with the text of the program from which the mentioned Ptree object was created.
void GetPtreePos(const Ptree *p, const char *&begin,
const char *&end) {
if (p == NULL)
return;
if (p->IsLeaf()) {
const char *pos = p->GetLeafPosition();
if (begin == NULL) {
begin = pos;
} else {
begin = min(begin, pos);
}
end = max(end, pos);
}
else {
GetPtreePos(p->Car(), begin, end);
GetPtreePos(p->Cdr(), begin, end);
}
}OpenC++ library doesn't support definition of variables of "const A (a)" type. To correct this defect a part of the code should be changed inside Parser::rOtherDeclaration function:
if(!rDeclarators(decl, type_encode, false))
return false;Instead of it the following code should be used:
if(!rDeclarators(decl, type_encode, false)) {
// Support: const A (a);
Lex::TokenIndex after_rDeclarators = lex->Save();
lex->Restore(before_rDeclarators);
if (lex->CanLookAhead(3) && lex->CanLookAhead(-2)) {
ptrdiff_t c_2 = lex->LookAhead(-2);
ptrdiff_t c_1 = lex->LookAhead(-1);
ptrdiff_t c0 = lex->LookAhead(0);
ptrdiff_t c1 = lex->LookAhead(1);
ptrdiff_t c2 = lex->LookAhead(2);
ptrdiff_t c3 = lex->LookAhead(3);
if (c_2 == CONST && c_1 == Identifier &&
c0 == '(' && c1 == Identifier && c2 == ')' &&
(c3 == ';' || c3 == '='))
{
Lex::TokenContainer newEmptyContainer;
ptrdiff_t pos = before_rDeclarators;
lex->ReplaceTokens(pos + 2, pos + 3, newEmptyContainer);
lex->ReplaceTokens(pos + 0, pos + 1, newEmptyContainer);
lex->Restore(before_rDeclarators - 2);
bool res = rDeclaration(statement);
return res;
}
}
}In this code some auxiliary functions are used which are not discussed in this article. But you can find them in VivaCore library.
Sometimes while programming one has to use workarounds to reach the desirable result. For example, a widely known macro "max" often causes troubles while defining in a class a method of "T max() {return m;}" type. In this case one resorts to some tricks and define the method as "T (max)() {return m;}". Unfortunately, OpenC++ doesn't understand such definitions inside classes. To correct this defect Parser::isConstructorDecl() function should be changed in the following way:
bool Parser::isConstructorDecl()
{
if(lex->LookAhead(0) != '(')
return false;
else{
// Support: T (min)() { }
if (lex->LookAhead(1) == Identifier &&
lex->LookAhead(2) == ')' &&
lex->LookAhead(3) == '(')
return false;
ptrdiff_t t = lex->LookAhead(1);
if(t == '*' || t == '&' || t == '(')
return false; // declarator
else if(t == CONST || t == VOLATILE)
return true; // constructor or declarator
else if(isPtrToMember(1))
return false; // declarator (::*)
else
return true; // maybe constructor
}
}OpenC++ library doesn't know that inside functions "using" and "namespace" constructions may be used. But one can easily correct it by modifying Parser::rStatement() function:
bool Parser::rStatement(Ptree*& st)
{
...
case USING :
return rUsing(st);
case NAMESPACE :
if (lex->LookAhead(2) == '=')
return rNamespaceAlias(st);
return rExprStatement(st);
...
}As it is known "this" is a pointer. But it's not so in OpenC++. That's why we should correct Walker::TypeofThis() function to correct the error of type identification.
Replace the code
void Walker::TypeofThis(Ptree*, TypeInfo& t)
{
t.Set(env->LookupThis());
}with
void Walker::TypeofThis(Ptree*, TypeInfo& t)
{
t.Set(env->LookupThis());
t.Reference();
}We have already mentioned Program::LineNumber() function when saying that it returns file names in different formats. Then we offered FixFileName() function to correct this situation. But LineNumber() function has one more disadvantage related to its slow working speed. That's why we offer you an optimized variant of LineNumber() function.
/*
LineNumber() returns the line number of the line
pointed to by PTR.
*/
size_t Program::LineNumber(const char* ptr,
const char*& filename,
ptrdiff_t& filename_length,
const char *&beginLinePtr) const
{
beginLinePtr = NULL;
ptrdiff_t n;
size_t len;
size_t name;
ptrdiff_t nline = 0;
size_t pos = ptr - buf;
size_t startPos = pos;
if(pos > size){
// error?
assert(false);
filename = defaultname.c_str();
filename_length = defaultname.length();
beginLinePtr = buf;
return 0;
}
ptrdiff_t line_number = -1;
filename_length = 0;
while(pos > 0){
if (pos == oldLineNumberPos) {
line_number = oldLineNumber + nline;
assert(!oldFileName.empty());
filename = oldFileName.c_str();
filename_length = oldFileName.length();
assert(oldBeginLinePtr != NULL);
if (beginLinePtr == NULL)
beginLinePtr = oldBeginLinePtr;
oldBeginLinePtr = beginLinePtr;
oldLineNumber = line_number;
oldLineNumberPos = startPos;
return line_number;
}
switch(buf[--pos]) {
case '\n' :
if (beginLinePtr == NULL)
beginLinePtr = &(buf[pos]) + 1;
++nline;
break;
case '#' :
len = 0;
n = ReadLineDirective(pos, -1, name, len);
if(n >= 0){ // unless #pragma
if(line_number < 0) {
line_number = n + nline;
}
if(len > 0 && filename_length == 0){
filename = (char*)Read(name);
filename_length = len;
}
}
if(line_number >= 0 && filename_length > 0) {
oldLineNumberPos = pos;
oldBeginLinePtr = beginLinePtr;
oldLineNumber = line_number;
oldFileName = std::string(filename,
filename_length);
return line_number;
}
break;
}
}
if(filename_length == 0){
filename = defaultname.c_str();
filename_length = defaultname.length();
oldFileName = std::string(filename,
filename_length);
}
if (line_number < 0) {
line_number = nline + 1;
if (beginLinePtr == NULL)
beginLinePtr = buf;
oldBeginLinePtr = beginLinePtr;
oldLineNumber = line_number;
oldLineNumberPos = startPos;
}
return line_number;
}In some cases Program::ReadLineDirective() function glitches taking irrelevant text for "#line" directive. The corrected variant of the function looks as follows:
ptrdiff_t Program::ReadLineDirective(size_t i,
ptrdiff_t line_number,
size_t& filename, size_t& filename_length) const
{
char c;
do{
c = Ref(++i);
} while(is_blank(c));
#if defined(_MSC_VER) || defined(IRIX_CC)
if(i + 5 <= GetSize() &&
strncmp(Read(i), "line ", 5) == 0) {
i += 4;
do{
c = Ref(++i);
}while(is_blank(c));
} else {
return -1;
}
#endif
if(is_digit(c)){ /* # <line> <file> */
unsigned num = c - '0';
for(;;){
c = Ref(++i);
if(is_digit(c))
num = num * 10 + c - '0';
else
break;
}
/* line_number'll be incremented soon */
line_number = num - 1;
if(is_blank(c)){
do{
c = Ref(++i);
}while(is_blank(c));
if(c == '"'){
size_t fname_start = i;
do{
c = Ref(++i);
} while(c != '"');
if(i > fname_start + 2){
filename = fname_start;
filename_length = i - fname_start + 1;
}
}
}
}
return line_number;
}Of course, this article covers only a small part of possible improvements. But we hope that they will be useful for developers while using OpenC++ library and will become examples of how one can specialize the library for one's own tasks.
We'd like to remind you once more that the improvements shown in this article and many other corrections can be found in VivaCore library's code. VivaCore library may be more convenient for many tasks than OpenC++.
If you have questions or would like to add or comment on something, our Viva64.com team is always glad to communicate. We are ready to discuss appearing questions, give recommendations and help you to use OpenC++ library or VivaCore library. Write us!
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