相同的声明以不同的顺序在gcc中产生不同的结果

Question

The problem is in line 7: int ret=3, x, y;

if I declare the y first (like the line 8) the result will be different

on my computer right now is printing only the Y values​​, with this change in the declaration goes to print only the values ​​of X

Makefile

gcc -g -o open_file_test open_file_test.c;
./pen_file_test input

CODE:

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

int worldsize = 0;

int main(int argc, char const *argv[]){
    int ret=3, x, y;
    //int ret=3, y, x;
    char chr;
    int teste;

    FILE * inputFile;
    inputFile = fopen(argv[1],"r");
    teste = fscanf(inputFile,"%d", &worldsize);
    printf("Tamanho: %d\n", worldsize);

    while(1){
        ret=fscanf(inputFile,"%d %d %s\n", &x, &y, &chr);
        if(ret != 3)
            break;
        printf("x: %d  y: %d\n", x, y);
    }
    printf("End File :D\n");
    return 0;
}

input_file

 10 1 0 w 2 1 s 6 9 w 3 7 w 5 0 s 1 5 t 1 5 t 7 5 t 9 7 t 9 3 t 0 0 i 

output

 Tamanho: 10 x: 0 y: 0 x: 0 y: 1 x: 0 y: 9 x: 0 y: 7 x: 0 y: 0 x: 0 y: 5 x: 0 y: 5 x: 0 y: 5 x: 0 y: 7 x: 0 y: 3 x: 0 y: 0 End File :D 

On my computer only read the Y, and the same code on my colleague computer only reads X, and in another friend's computer works fine (read the X and Y), can somebody explain the reason?

Answer 1

You have undefined behaviour in your code here:

fscanf(inputFile,"%d %d %s\n", &x, &y, &chr);

Reading a string into chr which is a single char variable. Even if the string contains a single character, a null-terminator will be written after it. This may well be spilling into your integers on the stack.

If you want a single char, then use %c :

fscanf(inputFile,"%d %d %c\n", &x, &y, &chr);

If you prefer a string, then make chr a char array large enough to hold any potential string (plus a null terminator). Alternatively, use fgets to read a line at a time and then parse the values out later.

Answer 2

On this line:

ret=fscanf(inputFile,"%d %d %s\n", &x, &y, &chr);

Your fscanf format has %s , which means "String" (several characters, ending with a NULL-terminator) , but the matching variable for the data, chr is only a single character, and cannot handle multiple characters.

To fix it, I recommend using formatter %c (which means a single character) instead of %s .