原来函数入参类型不匹配gcc也能编译通过啊-优快云博客

本文链接：https://blog.youkuaiyun.com/happen23/article/details/127307005

背景

前一段时间赶工修一个段错误的BUG，修复后代码不再有段错误，但却会导致板子软件与上位机断链，而且还是概率性的。
经过一周的排查，原来是修BUG时引入一个传参错误，给期待struct *形参的函数传了个struct **的实参，导致踩内存，又因为赶工，没仔细看编译告警，于是坑了自己。

复现过程

复现代码：

#include<stdio.h>

void change_info(int *p)  // 形参期待一级指针
{
    *p = 42;
}

int main() {
    int a = 0;
    int *pa = &a;

    printf("a == %d\n", a);
    change_info(&pa);  // 实参传递二级指针，会导致内存访问越界，即踩内存！
    printf("a == %d\n", a);
    return 0;
}

上面代码gcc编译通过，但有告警，说指针类型不匹配：

isp@ax:~/demo$ gcc test_2nd_ptr2.c
test_2nd_ptr2.c: In function ‘main’:
test_2nd_ptr2.c:13:17: warning: passing argument 1 of ‘change_info’ from incompatible pointer type [-Wincompatible-pointer-types]
     change_info(&pa);
                 ^
test_2nd_ptr2.c:3:6: note: expected ‘int *’ but argument is of type ‘int **’
 void change_info(int *p)
      ^~~~~~~~~~~

如果编译的文件很多，很容易忽略这些告警

上面问题代码的运行效果：

isp@ax:~/demo$ ./a.out
a == 0
a == 0

如何规避

用g++编译器无此问题，直接报error

isp@ax:~/demo$ g++ test_2nd_ptr2.c
test_2nd_ptr2.c: In function ‘int main()’:
test_2nd_ptr2.c:13:18: error: invalid conversion from ‘long long int’ to ‘int*’ [-fpermissive]
     change_info(l);
                  ^
test_2nd_ptr2.c:3:6: note:   initializing argument 1 of ‘void change_info(int*)’
 void change_info(int *p)
      ^~~~~~~~~~~
test_2nd_ptr2.c:15:20: error: cannot convert ‘int**’ to ‘int*’ for argument ‘1’ to ‘void change_info(int*)’
     change_info(&pa);
                    ^

给gcc传递-Werror选项也能避免此问题

isp@ax:~/demo$ gcc -Werror test_2nd_ptr2.c
test_2nd_ptr2.c: In function ‘main’:
test_2nd_ptr2.c:13:17: error: passing argument 1 of ‘change_info’ from incompatible pointer type [-Werror=incompatible-pointer-types]
     change_info(&pa);
                 ^
test_2nd_ptr2.c:3:6: note: expected ‘int *’ but argument is of type ‘int **’
 void change_info(int *p)
      ^~~~~~~~~~~
cc1: all warnings being treated as errors