Buffered And Non Buffered I O

• non-buffered IO directly outputs the data that is just inputed.
• buffered IO stores the inputed data into a buffer, and outputs a whole block of data when the buffer is full.

int main()
{
    printf("test1");
    fprintf(stderr, "test2");
    fprintf(stdout, "test3");
    printf("\n");
    fprintf(stderr, "\n");
    return 0;
// ./a > t1     
// ./a 2> t2
// ./a
}

test2test1test3

sosoman@sosoman:/tmp$ ./a 1>log 2>&1
sosoman@sosoman:/tmp$ cat log
test2
test1test3