Content written before fork() present in output twice

问题

I wrote the following C code:

#include<stdio.h>

int main(){
    printf("A");
    if(fork() == 0){
        printf("B");
    }
    else{
        printf("C");
    }
}

The output I got is:

ACAB

I expected this code to print A only once.
Can anyone explain this output?

回答1:

Your error is not flushing the buffers before fork-ing, thus both processes will write it.

Add this before fork():

fflush(0); // Flush all output-streams

回答2:

The 'A' is stored in a buffer and flushed by both processes when they exit.

来源：https://stackoverflow.com/questions/26162492/content-written-before-fork-present-in-output-twice