Question

I’m trying to understand some differences in file i/o techniques. Suppose I have the following code:

FILE *work_fp;
char record[500] = {0};
while(!feof(work_fp))
{
    static int first = 1;
    fgets(record, 200, work_fp);

    if (first)
    {
        var1 = 2;
        length += var1;
    }
    first = 0;

    if (feof(work_fp))
    {
        continue;
    }
    if((int)strlen(record) < length)
    {
        fclose(work_fp);
        std::ostringstream err;
        err << "ERROR -> Found a record with fewer bytes than required in file."
            << std::endl;
        throw std::runtime_error(err.str());
    }
    const int var2 = 1;
    if(memcmp(argv[1], record + var2, 3) == 0)
    {
        load_count_struct(record, var1);
    }
}

I’m not seeing how the second if argument can be true.

if (feof(work_fp))
{
    continue;
}

If feof(work_fp) is true wouldn’t the while argument be false? Then the continue could never get called?

FOLLOW UP QUESTION:

Ok, I see how fgets can cause work_fp to reach eof conditions.

Suppose I want to try and implement this another way. Using getline(), for example.

std::string data(file);
std::ifstream in(data.c_str());

if (!in.is_open())
{
    std::ostringstream err;
    err << "Cannot open file: " << file << std::endl;
    throw std::runtime_error(err.str());
}

std::string buffer = "";
std::string record = "";
while (getline(in, buffer))
{
    static int first = 1;

    if (first)
    {
        var1 = 2;
        length += var1;
    }
    first = 0;

    if (//What should go here?!?)
    {
        break;
    }
    // etc...
}

Any suggestions? I’m thinking

if (buffer == std::string::npos)

no?

Answer 1

The line:

fgets(record, 200, work_fp);

can advance to read/write head to the end of the file, thus changing the return value on feof.