将字符写入文件C ++

Question

I have a function that writes random numbers into a file while reading another file.

void writeFile() {
    FILE* file = fopen(source, "r");
    FILE* file2 = fopen(target, "w");
    srand (time(NULL));

    while (!feof(file)) {
        fgetc(file);
        fputc(0 + ( rand() % ( 50 - 0 + 1 ) ), file2);
    }


    fclose(file);
    fclose(file2);
}

The two files should have the same size. What happens is that the second file has more 1byte at the end compared with the first file. How can I avoid this?

Answer 1

As well as the EOF comments, you should also open both files in binary mode

FILE* file = fopen(source, "rb");
FILE* file2 = fopen(target, "wb");

In non-binary mode line endings may be translated (depending on platform). This potentially changes the number of characters read or written to a file.

Answer 2

Don't rely on feof to tell you that you've read all characters. Instead, check the return value from fgetc :

while (fgetc(file) != EOF) {
    fputc(0 + ( rand() % ( 50 - 0 + 1 ) ), file2);
}

Answer 3

The very final fgetc(file) reads EOF, then your code writes a byte for it into the new file and only then it tests for feof in the while .

Don't use feof , use this instead:

if (fgetc(file) == EOF) break;