Question

I’ve a very simple function that should read a txt file and return all lines by one vector of the type string. I’ve stepped trough it quite a few times with the debugger and the only thing i’ve noticed is that the value of “fileName” changes on the line of the ifstream declaration. What am i doing wrong?? Thx.

vector<string> readFile(char* fileName)
{
    vector<string> fileLines;
    fileLines.clear();
    string line;
    ifstream myfile (fileName);
    if (myfile.is_open())
    {
        while ( myfile.good() )
        {
            getline (myfile,line);
            fileLines.push_back(line);
        }
        myfile.close();
    }
    return fileLines;
}

//////////////////////////////////

I have this function that should return the filenames of all txt files in the current directory.

   vector<char*> getFileList()
    {
        vector<char*> fileNames;
        fileNames.clear();
        WIN32_FIND_DATA FindFileData;
        HANDLE hFind = INVALID_HANDLE_VALUE;
        char currentPath[_MAX_PATH];
        getCurrentPath(currentPath);
        strncat(currentPath, "\\*", 3);
        if (hFind = FindFirstFile(currentPath, &FindFileData))
        {

            string fileExtension = getExt(FindFileData.cFileName);
            if (fileExtension == "txt" || fileExtension == "TXT")
            {
                fileNames.push_back(FindFileData.cFileName);
            }
            while(FindNextFile(hFind, &FindFileData) != 0)
            {
                string fileExtension = getExt(FindFileData.cFileName);
                if (fileExtension == "txt" || fileExtension == "TXT")
                    fileNames.push_back(FindFileData.cFileName);
            }
        }
        return fileNames;
    }

That’s how the function is going to be called:

vector<char*> inputFileList = getFileList();
if (inputFileList.size() > 0)
{
    for (int a=0; a<inputFileList.size(); a++)
    {
        fileLines = readFile(inputFileList[a]);
    }
}

Answer 1

My bet would be that you get your filename from a function which returns a pointer to a local variable, e.g. something like this:

char * getFilename() {
 char Filename[100] = "/foo";
 return Filename;
} 

The above isn’t valid – Filename contents are on stack, and will be invalidated when getFilename() returns. vector<string> fileLines; will be located in the same memory, and therefore the data fileName points to will change when you step over the vector constructor.

EDIT: See e.g. C++ compiler warning – returning local variable for more information on this