Can anyone explain how the below mentioned scanf part will execute in while loop for getting matrix input without boundary size in C?

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

int main() {
    char s[10000];
    int a[100][100], rows = 0, cols = 0;
    while (scanf("%[^\n]\n", s) == 1) {
        char *num = strtok(s, " ");
        int val = 0;
        while (num != NULL) {
            a[rows][val  ] = atoi(num);
            num = strtok(NULL, " ");
        }
        rows  ;
        cols = val;
    }
    for (int j = 0; j < cols; j  ) {
        for (int i = 0; i < rows; i  )
            printf("%d ", a[i][j]);
        printf("\n)
    }
}

CodePudding user response：

how the below mentioned scanf part will execute ...

scanf("%[^\n]\n",s) weakly attempts to read a line of input.

Code then uses strtok() to find tokens which are then parsed with atoi().

Code contains weaknesses.

Incorrect reading a a line of user input

"%[^\n]" fails if the first character is '\n'. Else it reads an unlimited number of non-'\n' characters into s, then appending a null character. "\n" then reads in, and discards, 0 to an unlimited number of white-spaces including '\n', ' ', etc.

while(scanf("%[^\n]\n",s)==1){ will stop the loop if the first line is only "\n", but will silently consume "\n" otherwise. Lacking a width, it it worse than gets().

Perhaps scanf("