Printing the first 10 line of a file in C

Question

I'm new to programming in C. And I'm trying to print the first 10 lines of a text file. When I run my program with a text file containing 11 lines of text, only the first line is displayed. I'm not sure why it does that, but I suspect there is something wrong in my while loop. Can someone please help me?

#include <stdio.h>

int main(int argc, char *argv[]){
    FILE *myfile;
    char content;
    int max = 0;

    // Open file
    myfile = fopen(argv[1], "r");
    if (myfile  == NULL){
        printf("Cannot open file \n");
        exit(0);
}
    // Read the first 10 lines from file
    content  = fgetc(myfile);
    while (content != EOF){
        max++;
        if (max > 10)
            break;
        printf ("%c", content);
        content = fgetc(myfile);
    }
 
    fclose(myfile);
    return 0;
}

As a side note, consider calling `perror(argv[1])` instead of `printf("Cannot open file \n")`. It explains _why_ the file could not be opened. Also, make sure that `argv[1]` exists: `if (argc<=1) error...`. — DYZ, Jul 12 '21 at 03:39
What do *you* want your code to do if no filename is given on the command line? — Jeff Holt, Jul 12 '21 at 03:41

DYZ · Answer 1 · 2021-07-12T03:35:00.663

2

You have been already advised to use fgets. However, if your file has lines of unknown length, you may still want to use fgetc. Just make sure you count only newlines, not all characters:

int max = 0;
int content;
while ((content = fgetc(myfile)) != EOF && max < 10){
    if (content == '\n') max++;
    putchar(content);
}

edited Jul 12 '21 at 03:35

answered Jul 12 '21 at 03:31

DYZ

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score 1 · Answer 2 · answered Jul 12 '21 at 02:37

fgetc() returns the next character in the file, not the next line. You probably want to use fgets() instead, which reads up to the next newline character into a buffer. Your code should probably end up with something like:

// allocate 1K for a buffer to read
char *buff = malloc(1024);
// iterate through file until we are out of data or we read 10 lines
while(fgets(buff, 1024, myfile) != NULL && max++ < 10) {
    printf("%s\n", buff);
}
free(buff);
// close your file, finish up...

Read more about fgets() here: https://www.tutorialspoint.com/c_standard_library/c_function_fgets.htm

Thank you for taking the time to help me with my problem, for providing a solution, and the additional contents. I appreciate it. — Tom, Jul 12 '21 at 03:04

score 1 · Answer 3 · answered Jul 12 '21 at 03:15

fgetc function reads the next character not the next ine. for reading the number of lines you should use fgets function. this function reads the full string till the end of the one line and stores it in a string. your code Shuld be as:-

#include <stdio.h>

int main(int argc, char *argv[])
{
    FILE *myfile;
    char content[200];
    int max = 0;

    // Open file
    myfile = fopen(argv[1], "r");
    if (myfile == NULL)
    {
        printf("Cannot open file \n");
        exit(0);
    }
    // Read the first 10 lines from file
    fgets(content, 200, myfile);
    while (content != EOF)
    {
        max++;
        if (max > 10)
            break;
        printf("%s", content);
        fgets(content, 200, myfile);
    }

    fclose(myfile);
    return 0;
}

Thank you for taking the time to help me with my problem and for providing a clear solution. — Tom, Jul 12 '21 at 03:26
`while (content != EOF)` is the wrong test. Test the return value of `fgets()`. `content != EOF` compares a pointer to an `int`. Tip: enable all compiler warnings. — chux - Reinstate Monica, Jul 12 '21 at 03:30

Printing the first 10 line of a file in C

3 Answers3