CODEWITHSUNDEEP
cfile
Jared
Jared

Reputation: 25

read the last N lines from a file

I am trying to get this piece of code to read a line from a file but it's not working. I was wondering if one of you could help me. It was going to read the last 5 lines which I can configure later, but right now I am just trying to get it to read the last line.

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

int main() {
    FILE *myfile = fopen("X:\\test.txt", "r");
    int x, number_of_lines = 0, count = 0, bytes = 512, end;
    char str[256]; 

    do {
        x = fgetc(myfile);
        if (x == '\n')
            number_of_lines++;
    } while (x != EOF);    //EOF is 'end of file'

    if (x != '\n' && number_of_lines != 0)
        number_of_lines++;

    printf("number of lines in test.txt = %d\n\n", number_of_lines);

    for (end = count = 0; count < number_of_lines; ++count) {
        if (0 == fgets(str, sizeof(str), myfile)) {
            end = 1;
            break;
        }
    }

    if (!end)
        printf("\nLine-%d: %s\n", number_of_lines, str);

    fclose(myfile);
    system("pause");
    return 0;
}

Upvotes: 0

Views: 1990

Answers (2)

chqrlie
chqrlie

Reputation: 145307

Here is a simple solution where you read all lines into a circular line buffer and print the last 5 lines when the end of file has been reached:

#include <stdio.h>

int main(void) {
    char lines[6][256];
    size_t i = 0;
    FILE *myfile = fopen("X:\\test.txt", "r");

    if (myfile != NULL) {
        while (fgets(lines[i % 6], sizeof(lines[i % 6]), myfile) != NULL) {
            i++;
        }
        fclose(myfile);
        for (size_t j = i < 5 ? 0 : i - 5; j < i; j++) {
            fputs(lines[j % 6], stdout);
        }
    }
    return 0;
}

Upvotes: 1

Pedro Martins
Pedro Martins

Reputation: 11

Just make a for or while cycle that reads all the file(use fscanf) and when the reading gets to your desired line you save it to a var.

Upvotes: 1

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