函数里给传入指针分配空间可能导致的问题解决

写了一个读配置文件的接口，要取出类似"192.168.0.43\t80\thttps\tabc\n"的字符串的配置信息

 

思路：以\t为标识来分割字符串，用两个指针分别指向一个字段的头尾，然后写入传进来的指针里面

 

void get_cond(char *cond, char *ip, int *port, char *proto, char *txt)

{

              char *p, *p1, tmp[1024]={0};

              p = cond;

              p1 = cond;

              int flag = 0;

             

              while(*p != '\n'){

                     if(*p == '\t'){

                            flag ;

                            if(flag == 1){

                                   for(; p1 - p < 0; p1 ){

                                          sprintf(tmp strlen(tmp), "%c", *p1);

                                   }

                                   printf("%s\n",tmp);

                                   ip = strdup(tmp);

                                   printf("ip:%s\n", ip);

                                   sprintf(tmp, "");

                                   p1 ;     

                            }else if(flag == 2){

                                   for(; p1 - p < 0; p1 ){

                                          sprintf(tmp strlen(tmp), "%c", *p1);

                                   }

                                   printf("%s\n",tmp);

                                   port = atoi(tmp);

                                   printf("port:%d\n", port);

                                   sprintf(tmp, "");

                                   p1 ;     

                            }else if(flag == 3){

                                   for(; p1 - p < 0; p1 ){

                                          sprintf(tmp strlen(tmp), "%c", *p1);

                                   }

                                   printf("%s\n",tmp);

                                   proto = strdup(tmp);

                                   printf("proto:%s\n", proto);

                                   sprintf(tmp, "");

                                   p1 ;     

                                  

                                  

                            }

                     }

                     p ;

              }

              if(flag == 3){

                     for(; p1 - p < 0; p1 ){

                                          sprintf(tmp strlen(tmp), "%c", *p1);

                     }

                     printf("%s\n",tmp);

                     txt = strdup(tmp);

                     printf("txt:%s\n",txt);

              }

             

}

 

int main()

{

       char *ip, *proto, *txt;

       int port;

       char cond[] = "192.168.0.43\t80\thttps\tabc\n";

      

       get_cond(cond, ip, &port, proto, txt);

             

       printf("========ip:%s\n",ip);

       printf("========port:%d\n",port);

       printf("========proto:%s\n",proto);

       printf("========txt:%s\n",txt);

}

 

结果奇怪的是：在接口里面打印出来的字段都是正常的，但是在main函数里面调用之后，字段全部取的不正确了：

 打印了一下字段的地址，发现地址也变了，不知道是什么原因，后来仔细分析，找了问题所在：

  在main函数里面，传给调用函数get_cond的指针是没有内存空间的，该空间要在接口函数里面分配，但是函数调用完毕之后，这些指针就被释放掉了，所以，如果想使传进去的指针有效果，可以传入该指针的地址，如此一来，在接口函数里面分配空间，也就等于给指针分配了空间了。具体一点说，函数就可接口以改成这样：void get_cond(char *cond, char **ip, int *port, char **proto, char **txt)，里面具体代码就不贴了，有兴趣的朋友可以自己改好了试试，结果会如你所料的了。O(∩_∩)O~~