1.禁止隱式聲明

-Werror=implicit-function-declaration 編譯選項中加了這個，隱式聲明不過，報error而不是warning了

eg: test.c
int main(int argc, char *argv[])
{
    char *pstr = "hello nihao";
    printf("l pstr=%s\n", pstr);
}

[ubuntu @tmp]$ gcc test.c -o pp
test.c: In function ‘main’:
test.c:5:2: warning: incompatible implicit declaration of built-in
 
 function ‘printf’ [enabled by default]
  printf("l pstr=%s\n", pstr);


[ubuntu @tmp]$ gcc test.c -Werror=implicit-function-declaration  -o pp
test.c: In function ‘main’:
test.c:5:2: error: implicit declaration of function ‘printf’ [-Werror=implicit-function-declaration]
  printf("l pstr=%s\n", pstr);
  
 
^
test.c:5:2: warning: incompatible implicit declaration of built-in function ‘printf’ [enabled by default]
cc1: some warnings being treated as errors

編譯選項的使用