Determine if a file contains a string in C

Question

How can I check if a given FILE* contains a string in C running on Linux (if it matters)?

The string must consist of the whole line it's on. For example, this:

jfjfkjj
string
jfjkfjk

would be true; but this:

jffjknf
fklm...string...lflj
jfjkfnj

wouldn't. I'm essentially looking for an internal alternative to system("grep -x file")

Answer 1

This reads a file line by line and checks if the line matches the string supplied in argument 1 (argv[1]) after every read. If so, it sets the bool infile (bools defined in <stdbool.h>) to true.

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

int main(int argc, char **argv[]) {
    char    *filepath = "/path/to/file";
    bool    infile = false;
    char    *line = NULL;
    size_t  len = 0;
    ssize_t read;

    FILE    *fp = fopen(filepath, "r");

    if (!fp) {
        fprintf(stderr, "Failed to open %s\n", filepath);
        return 1;
    }

    while ((read = getline(&line, &len, fp)) != -1) {
        line[strcspn(line, "\n")] = 0;
        if (!strcmp(line, argv[1])) {
            infile = true;
            break;
        }
    }
    fclose(uuidfp);

    if (line)
        free(line);

    return 0;
}