C++ string 使用的深刻教训

//----------------------------------------------------

//AUTHOR: lanyang123456

//DATE: 2014-10-30

//---------------------------------------------------

server：

/*IPCsocket AF_UNIXserver*/#include <stdio.h>#include <sys/types.h>#include <sys/socket.h>#include <sys/un.h> #include <errno.h>#include <string.h>#include <unistd.h>#include <string>#define UNIX_DOMAIN"/tmp/UNIX.domain"#define QUEUE_LEN5using namespace std;struct message {int id;string strmsg;};int main(void){    socklen_t clt_addr_len;    int listen_fd;    int com_fd;    int ret;    int i;    char recv_buf[1024];     socklen_t len;    struct sockaddr_un client_addr;    struct sockaddr_un server_addr;     struct message req;    listen_fd = socket(PF_UNIX, SOCK_STREAM, 0);    if(listen_fd < 0)    {        perror("cannot create communication socket");        return -1;    }          //set server addr    server_addr.sun_family = AF_UNIX;    strncpy(server_addr.sun_path, UNIX_DOMAIN, sizeof(server_addr.sun_path) - 1);    unlink(UNIX_DOMAIN);    //bind sockfd & addr    ret = bind(listen_fd, (struct sockaddr*)&server_addr,sizeof(server_addr));    if(ret == -1)    {        perror("cannot bind server socket");        close(listen_fd);        unlink(UNIX_DOMAIN);        return -1;    }    //listen sockfd     ret = listen(listen_fd, 1);    if(ret==-1)    {        perror("cannot listen the client connect request");        close(listen_fd);        unlink(UNIX_DOMAIN);        return -1;    }    //have connect request use accept    len = sizeof(client_addr);    com_fd = accept(listen_fd, (struct sockaddr*)&client_addr, &len);    if(com_fd < 0)    {        perror("cannot accept client connect request");        close(listen_fd);        unlink(UNIX_DOMAIN);        return -1;    }    //read and printf sent client info    printf("-------accetpt client connect--------\n");         ret = read(com_fd, &req, sizeof(req));//req    if (ret <= 0)     {printf("write error(%d) %s\n", errno, strerror(errno));close(com_fd);    close(listen_fd);    unlink(UNIX_DOMAIN);    return -1;    }    printf("read client request.\n");    printf("strmsg.size() = %d\n",req.strmsg.size());    int msg_len = req.strmsg.size();    memset(recv_buf,0,1024);    ret = read(com_fd, recv_buf, msg_len);//body    if (ret <= 0)     {printf("write error(%d) %s\n", errno, strerror(errno));close(com_fd);    close(listen_fd);    unlink(UNIX_DOMAIN);    return -1;    }        req.strmsg.append(recv_buf, msg_len);    printf("Message from client : id: %d  body: %s\n", req.id, req.strmsg.c_str());     close(com_fd);    close(listen_fd);    unlink(UNIX_DOMAIN);    return 0;}

client：

/*IPCsocket AF_UNIXclient*/#include <stdio.h>#include <sys/types.h>#include <sys/socket.h>#include <sys/un.h>#include <errno.h>#include <string.h>#include <unistd.h>#include <string>#define UNIX_DOMAIN "/tmp/UNIX.domain"using namespace std;struct message {int id;string strmsg;};int main(void){    int connect_fd;    int ret;    char msg_body[1024];    int i;    static struct sockaddr_un server_addr;    struct message request;    //creat unix socket    connect_fd=socket(AF_UNIX, SOCK_STREAM, 0);    if(connect_fd<0)    {        perror("cannot create communication socket");        return 1;    }    server_addr.sun_family = AF_UNIX;    strcpy(server_addr.sun_path, UNIX_DOMAIN);    //connect server    ret=connect(connect_fd, (struct sockaddr*)&server_addr, sizeof(server_addr));    if(ret==-1)    {        perror("cannot connect to the server");        close(connect_fd);        return 1;    }    memset(msg_body, 0, 1024);    strcpy(msg_body, "message from client");    request.id = 101;    request.strmsg.append(msg_body, strlen(msg_body));    ret = write(connect_fd, &request, sizeof(request));//request    if (ret <= 0)     {printf("write error(%d) %s\n", errno, strerror(errno));close(connect_fd);return -1;    }    ret = write(connect_fd, msg_body, sizeof(msg_body));//body    if (ret <= 0)     {printf("write error(%d) %s\n", errno, strerror(errno));close(connect_fd);return -1;    }    close(connect_fd);    return 0;}<span style="font-size:14px;"></span>

$ g++ -o server server.cpp
$ g++ -o client client.cpp

./server
./client
server：
-------accetpt client connect--------
read client request.
Segmentation fault (core dumped)


分析：
从client接收string对象（假设为c），然后接收拷贝放到server端string对象（假设为s）中，server端string对象s相关地址是c对象中的地址；在server使用s对象引用地址，就存在内存越界问题（Segmentation fault）。
这是要深刻注意的！