Risk of printf(str)

The C Programming Language 2nd mentioned a subtle issue of printf: even if there is only one literal string to printf, do print it with format specifier "%s". The rule applies other similar print functions as well. The reason? Read on.

#include <stdio.h>

int main()
{
        char* str= "a string with % may not work\n";
        printf ("%s", str);
        printf (str);
        return 0;
}

[/home/lungangfang/tmp]./a.out
a string with % may not work
a string with Successay not work

[/home/lungangfang/tmp]gcc --version
gcc (GCC) 3.2.3 20030502 (Red Hat Linux 3.2.3-20)
Copyright (C) 2002 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.