Reading Files Line by Line in C

fgets() reads a line from a text stream into a bounded buffer. It is a simple way to process text or CSV files line by line without reading past the array capacity.

The original Plus2net example uses a sample CSV file. You can still download the sample test.csv file.

Read and Display Every Line Top ↑

#include <stdio.h>

int main(void) {
    FILE *file = fopen("test.csv", "r");
    char line[128];

    if (file == NULL) {
        perror("test.csv");
        return 1;
    }

    while (fgets(line, sizeof line, file) != NULL) {
        fputs(line, stdout);
    }

    fclose(file);
    return 0;
}

Read Only the First Line Top ↑

Key change: use one if instead of a loop when only the first line is required.

if (fgets(line, sizeof line, file) != NULL) {
    fputs(line, stdout);
}

Do Not Use feof() as the Loop Condition Top ↑

A common mistake is to loop on !feof(file). End-of-file is reported only after an attempted read reaches the end. Prefer testing the read operation itself:

while (fgets(line, sizeof line, file) != NULL) {
    /* process line */
}

Handle File-Open Errors Top ↑

#include <stdio.h>

int main(void) {
    FILE *file = fopen("missing.txt", "r");

    if (file == NULL) {
        perror("missing.txt");
        return 1;
    }

    fclose(file);
    return 0;
}

Read Structured Values with fscanf() Top ↑

#include <stdio.h>

int main(void) {
    FILE *file = fopen("products.txt", "r");
    int id;
    double price;

    if (file == NULL) {
        perror("products.txt");
        return 1;
    }

    while (fscanf(file, "%d %lf", &id, &price) == 2) {
        printf("Product ID: %d, Price: %.2f\n", id, price);
    }

    fclose(file);
    return 0;
}

Related File Tutorials Top ↑

• File Handling in C — complete hub
• Count line breaks and spaces in a file

Subhendu Mohapatra

Author & Instructor at plus2net

I write and maintain practical tutorials on Python, PHP, SQL, JavaScript, HTML, jQuery, and web development at plus2net. The tutorials focus on clear explanations, working examples, and code that readers can test and adapt while learning.

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