Outputting from file one line at a time

Question

I'm trying to output text from a file one line at a time. I'm currently hardcoding it and I have this so far:

int main(int argc, char *argv[])
{
    int x;
    int k;
    int limit = 5;
    FILE *file;

    file = fopen("C:\\Documents and Settings\\jon\\My Documents\\Visual Studio 2008\\Projects\\Project1\\Assignment8_2\\Debug\\TestFile1.txt", "r");
    if (file == NULL) {
     perror("Error");
    }

    for (k = 1; k <= limit; k++) {
     while ((x = fgetc(file)) != '\n') {
      printf("%c", x);
     }
    }
    fclose(file);
}

I was wondering where in the code above, if at all, I can check for EOF. I assume I need to do that, but not sure why. Still learning.... Thanks!

Answer 1

Maybe you can try this:

#include <iostream>
#include <iomanip>
#include <fstream>
using namespace std;

int main() {
    int sum = 0;
    int x;
    ifstream inFile;

    inFile.open("test.txt");
    if (!inFile) {
        cout << "Unable to open file";
        exit(1); // terminate with error
    }

    while (inFile >> x) {
        sum = sum + x;
    }

    inFile.close();
    cout << "Sum = " << sum << endl; 
    return 0;
}

Answer 2

you should check the eof from the output of fgetc:

...
x = fgetc(file);
while (x != '\n' && x != EOF) {
...

fgetc manual there

Answer 3

Smells like homework... check some of the many, many tutorials online. for example

Answer 4

If you can bound the maximum length of a line, fgets may be a better way to read each line; but since you mention C++, you might consider using, instead, getline (caveat: fgets also put the \n in the buffer it fills, getline doesn't). Both make easy to check for end of file (fgets returns NULL on eof, getline sets the eofbit on its istream argument, which it also returns).

Answer 5

fgets() for C, getline() for C++.

C:

#include <stdio.h>
#include <stdlib.h>

// adjust as appropriate
size_t const MAX_LINE_LENGTH = 1024;

int main()
{
    FILE * in;
    char line[ MAX_LINE_LENGTH ];
    if ( ( in = fopen( "test.txt", "r" ) ) == NULL )
    {
        puts( "Failed to open test.txt." );
        return EXIT_FAILURE;
    }
    while ( fgets( line, MAX_LINE_LENGTH, in ) != NULL )
    {
        printf( "%s", line );
    }
    fclose( in );
    return EXIT_SUCCESS;
}

C++:

#include <iostream>
#include <fstream>
#include <string>

int main()
{
    std::ifstream in( "test.txt" );
    std::string line;
    while ( getline( in, line ) )
    {
        std::cout << line << std::endl;
    }
    in.close();
    return 0;
}

Answer 6

you can call feof() to check for EOF or check if the return code for fgetc() matches EOF.

I'm adding both versions to your code although I'm not sure what the loops (especially the outer one) are supposed to do, but within the context of your sample, EOF checking would look like this..

/* EOF would now terminate both loops, using feof() and fgetc() return to check EOF */ 
for (k = 1; k <= limit && !feof(file); k++) {
    while ((x = fgetc(file))!='\n' && x!=EOF) {
            printf("%c", x);
    }
}