我正在尝试修改Linux tracepath（traceroute）程序，使其处理三个不同的ip地址。三个IP地址是：
它应该将它们转换为套接字地址结构和无符号整数值等，并且还可以转换为字符串，但我一直都会遇到seg错误。
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/socket.h>
#include <linux/types.h>
#include <linux/errqueue.h>
#include <errno.h>
#include <string.h>
#include <netdb.h>
#include <netinet/in.h>
//#include <resolv.h>
#include <sys/time.h>
#include <sys/uio.h>
#include <arpa/inet.h>
#include <getopt.h>
char target_ip_string[INET_ADDRSTRLEN] = {0}; // first address written out string
char alternate_ip_1[INET_ADDRSTRLEN] = {0}; // second address written out string
char alternate_ip_2[INET_ADDRSTRLEN] = {0}; // third address written out string
struct sockaddr_in target_host; // first address
struct sockaddr_in target_alt1; // second address
struct sockaddr_in target_alt2; // third address
/**
* This example should convert three distict ip addresses from three distinct
* strings to three distinct integer values.
*/
int
main(int argc, char **argv) {
setvbuf(stdout, NULL, _IONBF, 0); // auto flushing.
struct hostent *hostname_target_entry;
struct hostent *hostname_alt1_entry;
struct hostent *hostname_alt2_entry;
target_host.sin_family = AF_INET;
target_alt1.sin_family = AF_INET;
target_alt2.sin_family = AF_INET;
char * target_hostname = (char *) "11.11.11.11";
char * alternate_ip_1_local = (char *) "144.133.133.133";
char * alternate_ip_2_local = (char *) "202.202.202.202";
printf("The first ip is: %s \n", target_hostname);
printf("The second ip is: %s \n", alternate_ip_1_local);
printf("The third ip is: %s \n\n", alternate_ip_2_local);
hostname_target_entry = gethostbyname(target_hostname);
hostname_alt1_entry = gethostbyname(alternate_ip_1_local);
hostname_alt2_entry = gethostbyname(alternate_ip_2_local);
memcpy(&target_host.sin_addr, hostname_target_entry->h_addr_list[0], 4);
memcpy(&target_alt1.sin_addr, hostname_alt1_entry->h_addr_list[0], 4);
memcpy(&target_alt2.sin_addr, hostname_alt2_entry->h_addr_list[0], 4);
// These should be three different ip addresses
printf("First ip as an integer: %u \n", target_host.sin_addr.s_addr); // Why are these all the same?
printf("Second ip as an integer: %u \n", target_alt1.sin_addr.s_addr); // Why are these all the same?
printf("Third ip as an integer: %u \n\n", target_alt2.sin_addr.s_addr); // Why are these all the same?
printf("No seg fault yet. \n\n");
// This conversion should yield "11.11.11.11"
const char * conversion1 = inet_ntop(AF_INET, &(target_host.sin_addr), target_ip_string, INET_ADDRSTRLEN);
printf("Result of inet_ntop: %s \n", conversion1); // Why is this "202.202.202.202" and not "11.11.11.11"?
printf("Seg fault here. \n\n");
// This conversion should yield "144.133.133.133".
const char * conversion2 = inet_ntop(AF_INET, &(target_alt1.sin_addr), alternate_ip_1, INET_ADDRSTRLEN);
// This conversion should yield "202.202.202.202".
const char * conversion3 = inet_ntop(AF_INET, &(target_alt2.sin_addr), alternate_ip_2, INET_ADDRSTRLEN);
return 0;
}
终端输出：
The first ip is: 11.11.11.11
The second ip is: 144.133.133.133
The third ip is: 202.202.202.202
First ip as an integer: 3402287818
Second ip as an integer: 3402287818
Third ip as an integer: 3402287818
No seg fault yet.
Result of inet_ntop: 202.202.202.202
Seg fault here.
为什么我在字符串和hostent / sockaddr_in之间的转换和返回保持失败？
答案 0 :(得分：2)
gethostbyname函数返回一个指向静态数据的指针，因此如果你不复制给定调用的结果，它将被下一次调用覆盖。
由于您只是转换IP地址而非主机名，因此最好使用inet_addr代替：
target_host.sin_addr.s_addr = inet_addr("11.11.11.11");
target_alt1.sin_addr.s_addr = inet_addr("144.133.133.133");
target_alt2.sin_addr.s_addr = inet_addr("202.202.202.202");
答案 1 :(得分：0)
你走了。使用gethostbyname()的行都已使用#if 0进行了更正和注释。 （编辑检查“无法发生”的缓冲区溢出。）
#define _POSIX_C_SOURCE 200809L
#define _XOPEN_SOURCE 700
#define _ISOC99_SOURCE
#define _ISOC11_SOURCE
#include <assert.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/socket.h>
#include <string.h>
#include <netdb.h>
#include <netinet/in.h>
//#include <resolv.h>
#include <sys/time.h>
#include <sys/uio.h>
#include <arpa/inet.h>
#include <getopt.h>
char target_ip_string[INET_ADDRSTRLEN] = {0}; // first address written out string
char alternate_ip_1[INET_ADDRSTRLEN] = {0}; // second address written out string
char alternate_ip_2[INET_ADDRSTRLEN] = {0}; // third address written out string
struct sockaddr_storage target_host; // first address
struct sockaddr_storage target_alt1; // second address
struct sockaddr_storage target_alt2; // third address
/**
* This example should convert three distict ip addresses from three distinct
* strings to three distinct integer values.
*/
int
main(void) {
setvbuf(stdout, NULL, _IONBF, 0); // auto flushing.
#if 0
struct hostent hostname_target_entry;
struct hostent hostname_alt1_entry;
struct hostent hostname_alt2_entry;
const struct hostent* p;
#endif
struct addrinfo *hostaddr_temp = NULL;
char * target_hostname = (char *) "11.11.11.11";
char * alternate_ip_1_local = (char *) "144.133.133.133";
char * alternate_ip_2_local = (char *) "202.202.202.202";
printf("The first ip is: %s \n", target_hostname);
printf("The second ip is: %s \n", alternate_ip_1_local);
printf("The third ip is: %s \n\n", alternate_ip_2_local);
#if 0 /* Simple fix, but not thread-safe. */
p = gethostbyname(target_hostname);
memcpy( &hostname_target_entry, p, sizeof(struct hostent) );
p = gethostbyname(alternate_ip_1_local);
memcpy( &hostname_alt1_entry, p, sizeof(struct hostent) );
p = gethostbyname(alternate_ip_2_local);
memcpy( &hostname_alt2_entry, p, sizeof(struct hostent) );
#endif
/* The correct fix.
*/
/* Change AF_INET to AF_UNSPECIFIED to support IPv6: */
static const struct addrinfo hints = { .ai_flags = AI_NUMERICHOST, .ai_family = AF_INET };
if ( 0 == getaddrinfo( target_hostname, NULL, &hints, &hostaddr_temp ) ) {
/* The POSIX standard "guarantees" that a sockaddr_storage will always
* be big enough to hold any socket address, so this should never cause a
* buffer overflow, but ....
*/
assert( sizeof(target_host) >= hostaddr_temp[0].ai_addrlen );
memcpy ( &target_host, hostaddr_temp[0].ai_addr, hostaddr_temp[0].ai_addrlen );
freeaddrinfo(hostaddr_temp);
assert( AF_INET == target_host.ss_family );
}
else
perror("getaddrinfo");
if ( 0 == getaddrinfo( alternate_ip_1_local, NULL, &hints, &hostaddr_temp ) ) {
assert( sizeof(target_alt1) >= hostaddr_temp[0].ai_addrlen );
memcpy ( &target_alt1, hostaddr_temp[0].ai_addr, hostaddr_temp[0].ai_addrlen );
freeaddrinfo(hostaddr_temp);
assert( AF_INET == target_alt1.ss_family );
}
else
perror("getaddrinfo");
if ( 0 == getaddrinfo( alternate_ip_2_local, NULL, &hints, &hostaddr_temp ) ) {
assert( sizeof(target_alt2) >= hostaddr_temp[0].ai_addrlen );
memcpy ( &target_alt2, hostaddr_temp[0].ai_addr, hostaddr_temp[0].ai_addrlen );
freeaddrinfo(hostaddr_temp);
assert( AF_INET == target_alt2.ss_family );
}
else
perror("getaddrinfo");
hostaddr_temp = NULL;
// These should be three different ip addresses
const in_addr_t* const host_ipv4 = &((struct sockaddr_in*)(&target_host))->sin_addr.s_addr;
const in_addr_t* const alt1_ipv4 = &((struct sockaddr_in*)(&target_alt1))->sin_addr.s_addr;
const in_addr_t* const alt2_ipv4 = &((struct sockaddr_in*)(&target_alt2))->sin_addr.s_addr;
// printf("No seg fault yet. \n\n");
// This conversion should yield "11.11.11.11"
const char * conversion1 = inet_ntop(AF_INET, host_ipv4, target_ip_string, INET_ADDRSTRLEN);
printf("Result of inet_ntop: %s \n", conversion1);
// printf("Seg fault here. \n\n");
// This conversion should yield "144.133.133.133".
const char * conversion2 = inet_ntop(AF_INET, alt1_ipv4, alternate_ip_1, INET_ADDRSTRLEN);
printf("Result of inet_ntop: %s \n", conversion2);
// This conversion should yield "202.202.202.202".
const char * conversion3 = inet_ntop(AF_INET, alt2_ipv4, alternate_ip_2, INET_ADDRSTRLEN);
printf("Result of inet_ntop: %s \n", conversion3);
return 0;
}