从 C 文件中读取 - 输出错误

Question

I am writing a code to read from a file but it always prints wrong output.

The code is as follows:

int n;
struct threeNum num = { 0 };
FILE *fptr;

if ((fptr = fopen("input.txt", "rb")) == NULL) {
        printf("Error! opening file\n");

        // Program exits if the file pointer returns NULL.
        exit(1);
    }

for (n = 1; n < 5; ++n)
{
        fread(&num, sizeof(struct threeNum), 1, fptr);
        printf("n1: %d\tn2: %d\tn3: %d\n", num.n1, num.n2, num.n3);
}
fclose(fptr);

The struct is:

struct threeNum
{
    char n1, n2, n3;
};

And the.txt file is:

1 2 3
5 6 7
6 6 9
5 5 5
8 7 2

And I always get zeros printed.

Answer 1

fread reads binary objects, but your file is text. You need to read text and then parse that (such as with fscanf , or fgets followed by sscanf ).

Answer 2

// As @Arkku said, use fgets to read each line and sscanf to parse it. 
#include <stdio.h>
#include <stdlib.h>

int main() {
int num[15];
int totalRead, i = 0;
char dataToRead[50];
FILE *fp;

if ((fp = fopen("file.txt", "r")) == NULL) {
        printf("Error! opening file\n");
        // Program exits if the file pointer returns NULL.
        exit(1);
    }
// read the file
while (fgets(dataToRead, 50, fp) != NULL) {
    totalRead = sscanf(dataToRead, "%d%d%d", &num[i], &num[i+1], &num[i+2]);
    puts(dataToRead);
    i = i + 3;
}
// I used modulo so that after every 3rd element there is a newline
for (i = 0; i < 15; i++) {
    printf("%d ", num[i]);
    if ((i+1) % 3 == 0)
        printf("\n");
}
return 0;
}