What is wrong with my code? C language

Question

What is wrong with my code? The first line is correct from input.txt but the second is broken, and I don't know why date spends a line. Why do elements pack and method pick a date?

My code:

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

int main(int argc, const char * argv[]) {

    FILE *fr;
    char date[11];
    char pack[3], method[4];

    fr = fopen("input.txt","r");

    if(fr == NULL)
        printf("File not found\n");

    while(!feof(fr)) {
        fgets(date,11,fr);
        fgets(pack, 3, fr);
        fgets(method, 4, fr);
        printf("%s %s %s",date,pack,method);
    }

    fclose(fr);
    return 0;
}

My input.txt:

2015-05-01 A GG
2015-05-02 H GG
2015-05-03 H AA
2015-05-05 G SS
2015-05-06 D GG
2015-05-17 V GG
2015-05-24 AAAAA
2015-05-29 V GG
2015-06-01 V GG

And maybe somebody knows how to read the date format (not like in my code) from a file, and how to check if it is the next month or not?

Compile with all warnings and debug info (`gcc -Wall -Wextra -g`) then use a debugger (`gdb`). Your "find my bug in my program" question is off-topic here. — Basile Starynkevitch, Dec 26 '15 at 14:13
and you have so many bugs.... it may be categorized as too broad. too.. :) — Sourav Ghosh, Dec 26 '15 at 14:14
http://stackoverflow.com/questions/5431941/why-is-while-feof-file-always-wrong — Mat, Dec 26 '15 at 14:15
Besides, `fgets()` is not a good function to use. In this case, you can use `fscanf()` to get words separated by space. — Paulo, Dec 26 '15 at 14:15
`AAAAA` won't fit in `char method[4]`. What do you want to do for that line? — MikeCAT, Dec 26 '15 at 14:15
@MikeCAT for this line, code need to write "ignored" but it will be later. Now I just need read all elements from a file, and Date should be in ISO format — Baivaras, Dec 26 '15 at 14:20
@JohnBode Like this: 2015-02-01 S MR 20 15-02-02 S MR 2015-02-03 L LP 2015-02-05 S LP 20 15-02-06 S MR 2015-02-06 L LP 2015-02-07 L MR 20 15-02-08 M MR — Baivaras, Dec 26 '15 at 14:22

score 0 · Accepted Answer · answered Dec 26 '15 at 15:38

There are several errors in your code, for example strings that are too short, use of feof() and trying to use fgets() several times on the same text line in the file. While possible, it's not very clean, so I've use strtok() after reading a whole text line.

In this re-written code I have also detected when the month changes. I've used pointers to the data within the line. Please note that if you want to store the extracted data into arrays, you'll have to make such arrays and copy the data, because the data is overwritten on every line.

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

int main(int argc, const char * argv[])
{
    FILE *fr;
    char line[42];
    char *date, *pack, *method;
    int year, month, day, lastmonth = -1;

    if((fr = fopen("input.txt","r")) == NULL)
        exit(1);

    while(fgets(line, sizeof line, fr) != NULL) {   // instead of feof()

        pack = method = NULL;                       // preset to test later
        date = strtok(line, " \r\n\t");             // strip newline too
        if(date && strlen(date) == 10) {            // check valid substring
            year  = atoi(date);
            month = atoi(date+5);
            day   = atoi(date+8);
            printf("%04d-%02d-%02d", year, month, day);
            pack  = strtok(NULL, " \r\n\t");
            if(pack) {                              // was substring extracted?
                method  = strtok(NULL, " \r\n\t");
            }
            if (pack && method) {                   // were substrings extracted?
                printf(" %s %s", pack, method);
                if (month != lastmonth && lastmonth >= 0)
                    printf(" *New month*");
                }
            else {
                printf(" *Ignored*");
            }
            lastmonth = month;
            printf("\n");
        }
        else {
            printf("*Invalid line*\n");
        }
    }

    fclose(fr);
    return 0;
}

Program output:

2015-05-01 A GG
2015-05-02 H GG
2015-05-03 H AA
2015-05-05 G SS
2015-05-06 D GG
2015-05-17 V GG
2015-05-24 *Ignored*
2015-05-29 V GG
2015-06-01 V GG *New month*

Thank you very much ! You solved my problem – Baivaras Dec 27 '15 at 10:15 — Baivaras, Dec 27 '15 at 10:15

What is wrong with my code? C language

1 Answers1