int main() {
    FILE *fp= fopen("test","r");  //test.txt exists in the project; content: 11111;
    if (fp){
        int num;
        fscanf(fp,"%d",&num);
        printf("%d",num);
        fclose(fp);
    } else{
        printf("Null");
    }
    return 0;
}

输出：

//With "run" in IDE:
Null

//Using terminal in IDE:
(base) apple@xiaomibijiben-Air-3 untitled1 % clang main.c -o main   
(base) apple@xiaomibijiben-Air-3 untitled1 % ./main
11111%

我的猜测是：在终端中运行和运行选择不同的文件目录来读取。