V804. Decreased performance. The 'Foo' function is called twice in the specified expression to calculate length of the same string

24.06.2011

The analyzer detected a construct which can be potentially optimized. Length of one and the same string is calculated twice in one expression. For length calculation such functions as strlen, lstrlen, _mbslen, etc. are used. If this expression is calculated many times or strings have large lengths, this code fragment should be optimized.

For optimization purposes, you may preliminary calculate the string length and place it into a temporary variable.

For example:

if ((strlen(directory) > 0) &&
    (directory[strlen(directory)-1] != '\\'))

Most likely, this code processes only one string and it does not need optimization. But if the code is called very often, we should rewrite it. This is a better version of the code:

size_t directoryLen = strlen(directory);
if ((directoryLen > 0) && (directory[directoryLen-1] != '\\'))

Sometimes the V804 warning helps to detect much more crucial errors. Consider this sample:

if (strlen(str_1) > 4 && strlen(str_1) > 8)

An incorrect variable name is used here. This is the correct code:

if (strlen(str_1) > 4 && strlen(str_2) > 8)