linux网络编程笔记--inet-ntoa() 函数的返回值问题以及网络地址有效性的判断

今天学习了唐佐林老师的网络课程，记录一下发现的收获。

char *inet_ntoa(struct in_addr in); 
// 这个函数返回的指针是一块固定的空间, 使用的时候需要注意防止覆盖

demo :

#include 
#include 
#include 
#include 
#include 
#include 
#include 
int main()
{
    struct in_addr addr1 = {0x08070605};
    struct in_addr addr2 = {0x04030201};
    const char *s1 = inet_ntoa(addr1);
    printf("#line %d,addr1 = %sn",__LINE__,s1);
    const char *s2 = inet_ntoa(addr2);
    printf("#line %d,addr2 = %sn",__LINE__,s2);
    printf("----------------------------------n");
    printf("#line %d,addr1 = %s,pointer = %pn",__LINE__,s1,s1);
    printf("#line %d,addr2 = %s,pointer = %pn",__LINE__,s2,s2);
    printf("----------------------------------n");
    char *s11 = strcpy((char *)malloc(32),inet_ntoa(addr1));
    char *s12 = strcpy((char *)malloc(32),inet_ntoa(addr2));
    printf("#line %d,addr1 = %sn",__LINE__,s11);
    printf("#line %d,addr2 = %sn",__LINE__,s12);
    free(s11);
    free(s12);
}

root@jeason:~/network# g++ ntoa.cpp
root@jeason:~/network# ./a.out
#line 13,addr1 = 5.6.7.8
#line 15,addr2 = 1.2.3.4
----------------------------------
#line 17,addr1 = 1.2.3.4,pointer = 0x7f7c7a443550
#line 18,addr2 = 1.2.3.4,pointer = 0x7f7c7a443550
----------------------------------
#line 22,addr1 = 5.6.7.8
#line 23,addr2 = 1.2.3.4

#include 
#include 
#include 
#include 
#include 
#include 
#include 
int main()
{
    struct in_addr addr1;

    if(inet_aton("1.2.3.4",&addr1)){
        printf("#line %d,vaild addr .... addr1 = %xn",__LINE__,addr1.s_addr);
    }else{
        printf("#line %d,invaild addr ....n",__LINE__);
    }
    if(inet_aton("test str",&addr1)){
        printf("#line %d,vaild addr .... addr1 = %xn",__LINE__,addr1.s_addr);
    }else{
        printf("#line %d,invaild addr ....n",__LINE__);
    }
    return 0
}    

root@jeason:~/network# g++ ntoa.cpp
root@jeason:~/network# ./a.out
#line 13,vaild addr .... addr1 = 4030201
#line 20,invaild addr ....
root@jeason:~/network#