相关:《C指针截断问题(形如0xaaaabbbbccccdddd > 0xffffffffccccdddd)》 本篇送给每一位写C/C++的朋友。
试着编译这样一段程序
#include <stdio.h>
int *arr;
int main()
{
arr = malloc(sizeof(int));
return 0;
}
编译报错:
$ gcc -g a.c
a.c: In function 'main':
a.c:7:10: warning: implicit declaration of function 'malloc' [-Wimplicit-function-declaration]
7 | arr = malloc(sizeof(int));
| ^~~~~~
a.c:7:10: warning: incompatible implicit declaration of built-in function 'malloc'
a.c:2:1: note: include '<stdlib.h>' or provide a declaration of 'malloc'
1 | #include <stdio.h>
+++ |+#include <stdlib.h>
问题一:为什么编译器不报错?
问题二:不管这个告警会发生什么?
int malloc(int, size_t)
,这是非常危险的! 即从gcc -g a.c
升级为 gcc -g a.c -Werror
。
$ gcc -g a.c
a.c: In function 'main':
a.c:7:10: warning: implicit declaration of function 'malloc' [-Wimplicit-function-declaration]
7 | arr = malloc(sizeof(int));
| ^~~~~~
a.c:7:10: warning: incompatible implicit declaration of built-in function 'malloc'
a.c:2:1: note: include '<stdlib.h>' or provide a declaration of 'malloc'
1 | #include <stdio.h>
+++ |+#include <stdlib.h>
2 |
$ gcc -g a.c -Werror
a.c: In function 'main':
a.c:7:10: error: implicit declaration of function 'malloc' [-Werror=implicit-function-declaration]
7 | arr = malloc(sizeof(int));
| ^~~~~~
a.c:7:10: error: incompatible implicit declaration of built-in function 'malloc' [-Werror]
a.c:2:1: note: include '<stdlib.h>' or provide a declaration of 'malloc'
1 | #include <stdio.h>
+++ |+#include <stdlib.h>
2 |
cc1: all warnings being treated as errors