Question

ifstream::tellg() is returning -13 for a certain file.

Basically, I wrote a utility that analyzes some source code; I open all files alphabetically, I start with “Apple.cpp” and it works perfectly.. But when it gets to “Conversion.cpp”, always on the same file, after reading one line successfully tellg() returns -13.

The code in question is:

for (int i = 0; i < files.size(); ++i) { /* For each .cpp and .h file */
   TextIFile f(files[i]);
   while (!f.AtEof()) // When it gets to conversion.cpp (not on the others)
                      // first is always successful, second always fails
      lines.push_back(f.ReadLine());

The code for AtEof is:

    bool AtEof() {
        if (mFile.tellg() < 0)
            FATAL(format("DEBUG - tellg(): %d") % mFile.tellg());
        if (mFile.tellg() >= GetSize())
            return true;

        return false;
    }

After it reads successfully the first line of Conversion.cpp, it always crashes with DEBUG - tellg(): -13.

This is the whole TextIFile class (wrote by me, the error may be there):

class TextIFile
{
public:
    TextIFile(const string& path) : mPath(path), mSize(0) {
        mFile.open(path.c_str(), std::ios::in);

        if (!mFile.is_open())
            FATAL(format("Cannot open %s: %s") % path.c_str() % strerror(errno));
    }

    string GetPath() const { return mPath; }
    size_t GetSize() { if (mSize) return mSize; const size_t current_position = mFile.tellg(); mFile.seekg(0, std::ios::end); mSize = mFile.tellg(); mFile.seekg(current_position); return mSize; }

    bool AtEof() {
        if (mFile.tellg() < 0)
            FATAL(format("DEBUG - tellg(): %d") % mFile.tellg());
        if (mFile.tellg() >= GetSize())
            return true;

        return false;
    }

    string ReadLine() {
        string ret;
        getline(mFile, ret);
        CheckErrors();
        return ret;
    }

    string ReadWhole() {
        string ret((std::istreambuf_iterator<char>(mFile)), std::istreambuf_iterator<char>());
        CheckErrors();
        return ret;
    }

private:
    void CheckErrors() {
        if (!mFile.good())
            FATAL(format("An error has occured while performing an I/O operation on %s") % mPath);
    }

    const string mPath;
    ifstream mFile;
    size_t mSize;
};

Platform is Visual Studio, 32 bit, Windows.

Edit: Works on Linux.

Edit: I found the cause: line endings. Both Conversion and Guid and others had \n instead of \r\n. I saved them with \r\n instead and it worked. Still, this is not supposed to happen is it?

Answer 1

It’s difficult to guess without knowing exactly what’s in Conversion.cpp. However, using < with stream positions is not defined by the standard. You might want to consider an explicit cast to the correct integer type before formatting it; I don’t know what formatting FATAL and format() expect to perform or how the % operator is overloaded. Stream positions don’t have to map in a predicatable way to integers, certainly not if the file isn’t opened in binary mode.

You might want to consider an alternative implementation for AtEof(). Say something like:

bool AtEof()
{
    return mFile.peek() == ifstream::traits_type::eof();
}