character by character inconsistent response to \n

Question

I've been struggling with this bug for a while. I'm using windows 10 and code::blocks 16.01 MinGW.

I want to compare c to an end line character.

One program on my system runs successfully, just to skip the header line of a file:

while(c!='\n')
{
    c = fgetc(traverse);
    if(c == EOF)
        return(1);
}

where traverse was opened using

fopen("traverse.dat", "r");

however, my other programs:

FILE * infile;

/* Open a large CSV */
infile = fopen("Getty_Megatem.csv", "r");
if(infile == NULL)
{
    printf("no file");
    return(EXIT_FAILURE);
}
char c = 0;
int i = 0;

/* Opens file successfully */
printf("File opened\n");

/* Count commas in first line */
while(c != '\n');
{
    c = fgetc(infile);
    if(c == ',')
        i++;
    if(c == EOF)
        return(EXIT_FAILURE);
}

printf("Number of commas: %i\n", i);

fclose(infile);

return(EXIT_SUCCESS);

and

ifstream infile;
char c;
string mystr;

infile.open("ostring.dat");

// Skip a line
while (c!= '\n')
    infile >> c;

getline(infile, mystr);

and (the one I REALLY want to work)

ifstream emdata;

string firstline;
char c = 0;
int i = 0;

vector<double> vdata;

// redundancy 
vdata.reserve(10000);

// There are ~ 300 doubles per line
emdata.open("Getty_Megatem.csv");

// Skip first line
getline(emdata, firstline);

while(c != '\n' && c != EOF)
{
    emdata >> vdata[i] >> c;
    cout << vdata[i] << ",";
    i++;

    if(i == 999)
    {
        cout << "\n\ni>9999";
        break;
    }
}


emdata.close();
return 0;

are unsuccessful, they compile and execute then read the stream forever - or until my maximum iterations 9999 is reached. All these files contain new lines.

Answer 1

As pointed in the comments, the first one won't work because it have a ; right after the while(). The problem with the other two is that the >> operator don't read '\n' and spaces, they are treated as separators. That's why the last two won't work.

To fix the 1st just remove the ; after the while statement

//while(c != '\n');
while(c != '\n')
{
    c = fgetc(infile);
    if(c == ',')
        i++;
    if(c == EOF)
        return(EXIT_FAILURE);
}

And here are my suggestions for the others:

2nd - forget the while, if you want to skip a line, get a line and do nothing with it.

ifstream infile;
char c;
string mystr;

infile.open("ostring.dat");

// Skip a line
getline(infile, mystr);
/*while (c!= '\n')
    infile >> c;*/

getline(infile, mystr);

3rd - get the line and use stringstream to get the inputs you need

ifstream emdata;

string firstline;
char c = 0;
int i = 0;

vector<double> vdata;

// redundancy 
vdata.reserve(10000);

// There are ~ 300 doubles per line
emdata.open("Getty_Megatem.csv");

// Skip first line
getline(emdata, firstline);
//get second line
getline(emdata, firstline);
// replace commas with spaces
std::replace(firstline.begin(),firstline.end(),',',' ');
stringstream ss(firstline);//
while(ss.rdbuf()->in_avail()!=0)//loop until buffer is empty
{
    ss >> vdata[i];
    cout << vdata[i] << ",";
    i++;

    if(i == 999)
    {
        cout << "\n\ni>9999";
        break;
    }
}


emdata.close();
return 0;

Answer 2

You are using formatted input to get a character when you should be using unformatted input:

char c;
if (cin.get( c )) ...

or

int c;
c = cin.get();
if (c != cin.eof()) ...

The >> operator removes whitespace, including newlines.