文件程序-fseek不起作用

Question

I'm having trouble making this fseek() function work in my code. The text I wrote just doesn't start at the point I indicate and I don't know why. It should start writing from the \\n and it just overwrite all the text file. Even if I open it with a it just doesn't go where I command through the parameters.

   fclose(file);
    FILE *file_a = fopen("ex6.txt", "w");

    fseek(file_a, -1, SEEK_END);

    puts("Write text to add:");
    while((letter = getchar()) != '\n')
    {
        fputc(letter, file_a);
    };

What is happening? Why doesnt this work?

Answer 1

Navigating to absolute only works when the file is opened in binary mode. When it's opened in text mode, fseek() cannot navigate to absolute positions in a file besides 0 (the start of the file), and trying to do so will result in undefined behaviour. You can, however, navigate to references in the file returned by ftell() . The reason for this is due to the handling of certain characters by some operating systems; some implementations allow it but POSIX doesn't mandate it.

I know you solved the issue in the comments, this is just for closure.