C - 使用 fscanf 从文件中读取“-1”

Question

I'm a bit new to C, but basically I have a problem where I need to read '-1' from a file. Sadly this means I run into a premature ending of the file, because the EOF constant is also -1 in my compiler.

What sort of work arounds would there be for this? Is there another function I can use to read it that will change the EOF to something I can work with?

Thanks in advance.

The code since people are asking for it

int read() {
    int returnVal; // The value which we return

    // Open the file if it isn't already opened
    if (file == NULL) {
        file = fopen(filename, "r");
    }

    // Read the number from the file
    fscanf(file, "%i", &returnVal);

    // Return this number
    return returnVal;
}

This number is then later compared to EOF.

Okay this is probably bad practice, but I changed the code to the following

int readValue() {
    int returnVal; // The value which we return

    // Open the file if it isn't already opened
    if (file == NULL) {
        file = fopen(filename, "r");
    }

    // Read the number from the file
    fscanf(file, "%i", &returnVal);

    if (feof(file)) {
        fclose(file);
        return -1000;
    }

    // Return this number
    return returnVal;
}

Because I knew I would never read any such number from my file (they range from about [-300, 300]. Thanks for all your help guys!

Answer 1

fscanf 的返回值不是读取的值，而是成功读取的项目数，如果发生错误，则返回 EOF。

Answer 2

The problem is that your read function doesn't distinguish between a successful read and an error condition. You should change it to accept a int * as a parameter that scanf writes into, and the function should return something like 0 on a successful read and -1 on error. You can use the return value of scanf as the basis of what your function returns.

Also, there's a system call named read , so you should really name it something else. And don't forget to fclose(file) at the end of the function, otherwise you're leaking file descriptors.