C Read From a File

Suppose the file students.txt has this text.

Robin 85
Maria 92
John 78

Read line by line with fgets

#include <stdio.h>

int main(void) {
    FILE *fp = fopen("students.txt", "r");
    char line[100];

    if (fp == NULL) {
        printf("Cannot open the file\n");
        return 1;
    }
    while (fgets(line, sizeof(line), fp) != NULL) {
        printf("%s", line);
    }
    fclose(fp);
    return 0;
}

Output:

fgets() returns NULL at the end of the file, so the loop stops there.

Read formatted data with fscanf

#include <stdio.h>

int main(void) {
    FILE *fp = fopen("students.txt", "r");
    char name[20];
    int marks, total = 0;

    if (fp == NULL) return 1;
    while (fscanf(fp, "%19s %d", name, &marks) == 2) {
        printf("%s scored %d\n", name, marks);
        total += marks;
    }
    fclose(fp);

    printf("Total = %d\n", total);
    return 0;
}

Output:

Read character by character with fgetc

#include <stdio.h>

int main(void) {
    FILE *fp = fopen("students.txt", "r");
    int ch, lines = 0;

    if (fp == NULL) return 1;
    while ((ch = fgetc(fp)) != EOF) {
        if (ch == '\n') lines++;
    }
    fclose(fp);

    printf("Lines = %d\n", lines);
    return 0;
}

Output:

Store the result of fgetc() in an int, not in a char, because EOF is a special int value.

Next: C Command Line Arguments.

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