写入file.txt

#include <stdio.h>

int main() {
    FILE *fp;
    fp = freopen("file.txt", "w+", stdout);

    printf("该文本重定向到 file.txt\n");

    fclose(fp);
    return 0;
}

读取

#include<stdio.h>

int main() {
    FILE *fp;
    int c;

    fp = fopen("file.txt", "r");
    while (1) {
        c = fgetc(fp);
        if (feof(fp)) {
            break;
        }
        printf("%c", c);
    }
    fclose(fp);
    return (0);
}