使用C popen()：read()起作用，但fread()不起作用

#include <stdio.h>

int main() {
    FILE *fp;
    char buffer[1024];

    fp = popen("ls", "r");
    if (fp == NULL) {
        printf("Failed to run command\n");
        return 1;
    }

    while (fgets(buffer, sizeof(buffer), fp) != NULL) {
        printf("%s", buffer);
    }

    pclose(fp);

    return 0;
}

#include <stdio.h>

int main() {
    FILE *fp;
    char buffer[1024];

    fp = fopen("file.txt", "r");
    if (fp == NULL) {
        printf("Failed to open file\n");
        return 1;
    }

    fread(buffer, sizeof(char), sizeof(buffer), fp);
    printf("%s", buffer);

    fclose(fp);

    return 0;
}