套接字编程中的分段错误

Question

我正在尝试在 C 上编写一个简单的服务器-客户端通信程序。但是，只要客户端尝试连接到服务器，我就会不断在服务器端收到错误：

分段错误

服务器端代码是：

#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<sys/socket.h>
#include<sys/types.h>
#include<netinet/in.h>

void error(char *);

int main(int argc, char *argv[])
{
int sockfd, newsockfd, n, serv_size, cli_size, port_no, bindfd, readfd, writefd, listenfd;
char sbuffer[256];
char *p;
p = &sbuffer[0];    

struct sockaddr_in serv_addr, cli_addr;

if (argc < 2)
    error("No port no. Specified!\n");

//creating sever side socket    
sockfd = socket(AF_INET, SOCK_STREAM, 0);
if (sockfd == -1)
    error("Server side listening Socket could not be created!\n");


bzero((char *)&serv_addr, sizeof(serv_addr));
port_no = atoi(argv[1]);
serv_addr.sin_family =  AF_INET;
serv_addr.sin_port = htons(port_no);
serv_addr.sin_addr.s_addr = INADDR_ANY;

//binding socket
bindfd = bind(sockfd, (struct sockaddr *)&serv_addr, sizeof(serv_addr));
if  (bindfd == -1)
    error("Failed to bind server side socket!\n");

//listening for incoming connections
listenfd = listen(sockfd, 5);
if (listenfd == -1)
    error("Failed to lisen to incoming connections!\n");

serv_size = sizeof(serv_addr);
cli_size = sizeof(cli_addr);
newsockfd = accept(sockfd, (struct sockaddr *)&cli_addr, &serv_size);
if (newsockfd == -1)
    error("Failed to accept connections from client!\n");

printf("Server received connections from %s  \n", (char *)inet_ntoa(cli_addr.sin_addr));    
while(1)
{   
    bzero(p, sizeof(sbuffer));
    readfd = read(newsockfd, p, sizeof(sbuffer));
    if (readfd == -1)
        error("Sorry. Unable to read message from client!\n");
    printf("Message Received: ");
    puts(sbuffer);

    bzero(p,  sizeof(sbuffer));
    printf("\nEnter Your Message for client: ");
    gets(sbuffer);
    writefd = write(newsockfd, p, sizeof(sbuffer));
    if (writefd == -1)
        error("Sorry. Message Could not be sent to client.\n");
    printf("Congratulations! Message has been sent to client.\n");  
}       

return 0;   
}
void error(char *msg)
{
perror(msg);
exit(1);
}

客户端代码是：

#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<sys/socket.h>
#include<sys/types.h>
#include<netinet/in.h>
#include<netdb.h>

void error(char *);
int main(int argc, char *argv[])
{
int sockfd, newsockfd, port_no, n, connectfd, readfd, writefd;
char cbuffer[256];
char *ptr = &cbuffer[0];

struct sockaddr_in serv_addr;
struct hostent *he;

if (argc != 3)
    error("Incomplete arguments!\n");

port_no = atoi(argv[2]);
he = gethostbyname(argv[1]);
if (he == NULL)
    error("No Such Host!\n");

sockfd = socket(AF_INET, SOCK_STREAM, 0);
if(sockfd == -1)
    error("Sorry. Socket could not be created!\n");

bzero((char *)&serv_addr, sizeof(serv_addr));
serv_addr.sin_family = AF_INET;
serv_addr.sin_port = htons(port_no);
serv_addr.sin_addr = *((struct in_addr *)he->h_addr);  

connectfd = connect(sockfd, (struct sockaddr *)&serv_addr, sizeof(serv_addr));
if (connectfd == -1)
    error("Sorry. Could not connect to server.\n");

while(1)
{   
    bzero(ptr, sizeof(cbuffer));
    printf("\nEnter message for Server: \n");
    gets(cbuffer);
    writefd = write(sockfd, ptr, sizeof(cbuffer));
    if (writefd == -1)
        error("Sorry. Could not send message to Server.");

    printf("Congratulations! Server Successfully Received your message.\n");    

    bzero(ptr, sizeof(cbuffer));
    readfd = read(sockfd, ptr, sizeof(cbuffer));
    if (readfd == -1)
        error("Sorry. Message from server could not be read.\n");

    printf("Message Received: ");
    puts(cbuffer);
}
return 0;
}
void error(char *msg)
{
perror(msg);
exit(1);
}

这是我在编译 serv.c 时的编译时警告：

cc -o s serv.c 
serv.c: In function ‘main’:
serv.c:47:52: warning: cast to pointer from integer of different size [-Wint-to-pointer-cast]

附： ：我使用的是 Ubuntu 12.04，我实际编写了这些程序并成功执行了这些程序。但我最近迁移到 Linux Mint 13 Cinnamon。我重新编译了程序。可能他们也成功地在 Mint 上执行了。但现在它似乎以某种方式抓住了这个错误。

Answer 1

如果您在 64 位系统上运行，请自行调用；

printf("Server received connections from %s  \n", 
    (char *)inet_ntoa(cli_addr.sin_addr));    

...可能会中断。由于您没有包含<arpa/inet.h>，因此您没有inet_ntoa 的定义。这将使编译器假定它返回一个int。由于int 不一定是 64 位（实际上大多数机器似乎不是），它不足以存储返回的 char 指针，因此您的 printf 因无效字符串而崩溃。这发生在（例如）64 位 MacOS X 上。

只需简单地将#include <arpa/inet.h> 放在服务器中的包含中即可解决该问题。

您也不应忽略int 和socklen_t 之间的区别，并解决混淆cli_size 和serv_size 的问题，请阅读现有的cmets 和答案以了解更多信息。

Answer 2

我会说问题是缺少 inet_ntoa() 的原型。

这让编译器假设它返回int。

这会使应用程序崩溃：

printf("Server received connections from %s  \n", (char *)inet_ntoa(cli_addr.sin_addr));    

包含<arpa/inet.h> 的以下代码即使使用-Wall 也会在没有警告的情况下编译。

printf("Server received connections from %s  \n", inet_ntoa(cli_addr.sin_addr));