优化使函数立即返回而不是执行

Question

I'm working on VS 2010 express and trying to do some file reading and parsing work

my function goes something like this... (I dropped the boring parts)

void SomeClass::SomeFunc(char *ALName, std::map<...> *chromList, std::map<...> *chromLine)
{
    ifstream file;
    char tmpBuff[500];
    char tmpBuff2[500];
    char fileName[350];
    char tmp[350];
    char *pch;
    char *pch2;

    .....

    file.open(fileName);

    while ( file.getline( tmpBuff, 500 ) ) 
    {
        ....
        if ( some_condition == 0 )
        {
          pch2 = strtok( NULL, "," );
          pch = strtok( NULL, "," );
          (*chromList)[pch2] = do_some_work( atoi(pch), tmpBuff2 );
          strcpy( tmp, get_chrom_line( tmpBuff2 ) );
          (*chromLine)[pch2] = tmp;
        }
    }

    file.close();

 }

When I change to Release with Optimization set to Maximum speed this function is skipped. The debugger enters the function and immediately returns.

When i run with Debug setting or Release with the Optimization flag set to disabled, the function runs just fine.

What can be the possible reason for that? Can I put a preprocessor definition to force "No optimization" on this function while the rest of the code get optimized

Thanks!! Idan

Answer 1

You should never try to debug optimized code. The line numbers it shows you will rarely match up with what is actually being executed, and forget about reading local variables. That is why there is a "Debug" and "Release" mode.

However, if you really want to, try this to make Visual Studio not optimize that function. You could also put that function in a separate source file and compile it in debug mode.

Answer 2

Are you sure that the function is actually being skipped and that the debugger isn't simply making it look skipped?

If it really isn't being executed then it's almost certain you have undefined behavior that happens to work how you want it when not optimized and the compiler (probably rightfully) optimizes it into non-working code in optimized mode.

That said I see some questionable items: You call strtok with NULL (aside - prefer 0 or nullptr in C++/C++11) without calling it with a valid pointer. Are you aware that strtok is destructive?

Then you use a character pointer to index an array, or presumably (hopefully?) call an overloaded operator[] function with a char* argument.

Since this is C++, your code will be cleaner, safer, and probably easier to debug if you remove all the C-style parsing and do it with string and find / find_first_of /etc depending on your needs.