warning: function returns address of local variable
2013-12-09 18:11
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char *ip_proc(char *p2) { int i; long int num_res[4]; char result[16]; for(i=0;i<4;i++) { char temp[3]; memcpy(temp,p2+i*2,2); temp[2]='\0'; num_res[i]=strtol(temp,NULL,16); } sprintf(result,"%d.%d.%d.%d",num_res[0],num_res[1],num_res[2],num_res[3]); return result; }
在编译调用这个函数的程序时,产生一个warning,这个warning也正是自己想看到的,符合自己的预想:
我们知道一个函数的局部变量都是存在stack中的,当这个函数调用过程结束时,这个局部变量都是要释放掉的,所以就会产生这样的warning,这个是和变量的lifetime相关的,所以解决方法有:
1.将char result[16]改为static型
2.使用malloc向heap申请,这些是需要caller用free去释放的
这里其实我想到了string.h里很多函数都是返回char *的,比如strcat,strcpy,strchr等,看了看标准库里的实现,发现都是根据传进来的char *来返回的,比如strcat.c
#include <string.h> char *(strcat)(char *s1, const char *s2) { char *s; for(s=s1;*s!='\0';++s); for(;(*s=*s2)!='\0';++s,++s2); return (s1); }
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