error的含義是什么：取消引用指向不完整類型的指針

Question

這是我的計划：

//SSL-Server-Client-Linkage-Broker.c  
#include <errno.h>  
#include <unistd.h>  
#include <malloc.h>  
#include <string.h>
#include <asm/stat.h>
#include <linux/fs.h>
#include <linux/sched.h>
#include <arpa/inet.h>  
#include <sys/socket.h>  
#include <sys/types.h>  
#include <netinet/in.h>  
#include <resolv.h>  
#include "openssl/ssl.h"  
#include "openssl/err.h"  

#define FAIL    -1  

int OpenConnection(const char *hostnamen, int portn) //for software house 
{   int sd;  
    struct hostent *host;  
    struct sockaddr_in addr;  

    if ( (host = gethostbyname(hostnamen)) == NULL )  
    {  
        perror(hostnamen);  
        abort();  
    }  
    sd = socket(PF_INET, SOCK_STREAM, 0);  
    bzero(&addr, sizeof(addr));  
    addr.sin_family = AF_INET;  
    addr.sin_port = htons(portn);  
    addr.sin_addr.s_addr = *(long*)(host->h_addr);  
    if ( connect(sd, (struct sockaddr*)&addr, sizeof(addr)) != 0 )  
    {  
        close(sd);  
        perror(hostnamen);  
        abort();  
    }  
    return sd;  
}  

SSL_CTX* InitServerCTX(void)  
{   SSL_METHOD *method;  
    SSL_CTX *ctx;  

    OpenSSL_add_all_algorithms();  /* load & register all cryptos, etc. */  
    SSL_load_error_strings();   /* load all error messages */  
    method = SSLv2_server_method();  /* create new server-method instance */  
    ctx = SSL_CTX_new(method);   /* create new context from method */  
    if ( ctx == NULL )  
    {  
        ERR_print_errors_fp(stderr);  
        abort();  
    }  
    return ctx;  
}  



int OpenListener(int port)  
{   int sd;  
    struct sockaddr_in addr;  

    sd = socket(PF_INET, SOCK_STREAM, 0);  
    bzero(&addr, sizeof(addr));  
    addr.sin_family = AF_INET;  
    addr.sin_port = htons(port);  
    addr.sin_addr.s_addr = INADDR_ANY;  
    if ( bind(sd, (struct sockaddr*)&addr, sizeof(addr)) != 0 )  
    {  
        perror("can't bind port");  
        abort();  
    }  
    if ( listen(sd, 10) != 0 )  
    {  
        perror("Can't configure listening port");  
        abort();  
    }  
    return sd;  
}  



void LoadCertificates(SSL_CTX* ctx, char* CertFile, char* KeyFile)  
{  
 /* set the local certificate from CertFile */  
    if ( SSL_CTX_use_certificate_file(ctx, CertFile, SSL_FILETYPE_PEM) <= 0 )  
    {  
        ERR_print_errors_fp(stderr);  
        abort();  
    }  
    /* set the private key from KeyFile (may be the same as CertFile) */  
    if ( SSL_CTX_use_PrivateKey_file(ctx, KeyFile, SSL_FILETYPE_PEM) <= 0 )  
    {  
        ERR_print_errors_fp(stderr);  
        abort();  
    }  
    /* verify private key */  
    if ( !SSL_CTX_check_private_key(ctx) )  
    {  
        fprintf(stderr, "Private key does not match the public certificate\n");  
        abort();  
    }  
}  

void ShowCerts(SSL* ssl)  
{   X509 *cert;  
    char *line;  

    cert = SSL_get_peer_certificate(ssl); /* Get certificates (if available) */  
    if ( cert != NULL )  
    {  
        printf("Server certificates:\n");  
        line = X509_NAME_oneline(X509_get_subject_name(cert), 0, 0);  
        printf("Subject: %s\n", line);  
        free(line);  
        line = X509_NAME_oneline(X509_get_issuer_name(cert), 0, 0);  
        printf("Issuer: %s\n", line);  
        free(line);  
        X509_free(cert);  
    }  
    else  
        printf("No certificates.\n");  
}  

char Servlet(SSL* ssl) /* Serve the connection -- threadable */  
{   char buf[1024]; 
char bufnew[1024];  
    char reply[1024];  
    int sd, bytes;  
    const char* echo="Message received";  

    if ( SSL_accept(ssl) == FAIL )     /* do SSL-protocol accept */  
        ERR_print_errors_fp(stderr);  
    else  
    {  
        ShowCerts(ssl);        /* get any certificates */  
        bytes = SSL_read(ssl, buf, sizeof(buf)); /* get request */
        if ( bytes > 0 )  
        {  
            buf[bytes] = 0;  
            printf("Client msg: %s\n", buf);
    strcpy (bufnew,buf);  
            sprintf(reply, echo, buf);   /* construct reply */  
            SSL_write(ssl, reply, strlen(reply)); /* send reply */
    return bufnew;  /* storing that in buffer for sending it to software house */
        }  
        else  
            ERR_print_errors_fp(stderr);  
    }  
    sd = SSL_get_fd(ssl);       /* get socket connection */  
    SSL_free(ssl);         /* release SSL state */  
    close(sd);          /* close connection */  
}  



SSL_CTX* InitCTX(void)  
{   SSL_METHOD *method;  
    SSL_CTX *ctxn;  

    OpenSSL_add_all_algorithms();  /* Load cryptos, et.al. */  
    SSL_load_error_strings();   /* Bring in and register error messages */  
    method = SSLv2_client_method();  /* Create new client-method instance */  
    ctxn = SSL_CTX_new(method);   /* Create new context */  
    if ( ctxn == NULL )  
    {  
        ERR_print_errors_fp(stderr);  
        abort();  
    }  
    return ctxn;  
}  
int main(int count, char *strings[])  
{   SSL_CTX *ctx;  
    int server;  
    char *portnum;  
int servern;  
    char bufnew[1024];  
    int bytes;
    char *hostnamen, *portnumn;  


    if ( count != 2 )  
    {  
        printf("Usage: %s <portnum>\n", strings[0]);  
        exit(0);  
    }  
    SSL_library_init();  

    portnum = strings[1];  
    ctx = InitServerCTX();        /* initialize SSL */  
    LoadCertificates(ctx, "mycert.pem", "mycert.pem"); /* load certs */  
    server = OpenListener(atoi(portnum));    /* create server socket */  
    while (1)  
    {   struct sockaddr_in addr;  
        socklen_t len = sizeof(addr);  
        SSL *ssl;  

        int client = accept(server, (struct sockaddr*)&addr, &len);  /* accept connection as usual */  
        printf("Connection: %s:%d\n",inet_ntoa(addr.sin_addr), ntohs(addr.sin_port));  
        ssl = SSL_new(ctx);              /* get new SSL state with context */  
        SSL_set_fd(ssl, client);      /* set connection socket to SSL state */  
        Servlet(ssl);         /* service connection */  
    }  
    close(server);          /* close server socket */  
    SSL_CTX_free(ctx);         /* release context */  

/* ----------------------------- End of programmer/linkage broker connection ----------------------------------*/

/* ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Start of linkage broker/software house connection ~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/

SSL_CTX *ctxn; 
SSL *ssln;  
if ( count != 3 )  
    {  
        printf("usage: %s <hostnamen> <portnumn>\n", strings[0]);  
        exit(0);  
    }  
    SSL_library_init();  
    hostnamen = strings[1];  
    portnumn = strings[2];  

    ctxn = InitCTX();  
    server = OpenConnection(hostnamen, atoi(portnumn));  
    ssln = SSL_new(ctxn);      // create new SSL connection state 
    SSL_set_fd(ssln, server);    // attach the socket descriptor   
    if ( SSL_connect(ssln) == FAIL )   //perform the connection   
        ERR_print_errors_fp(stderr);  
    else  
    {   char *msg = bufnew;

        printf("Connected with %s encryption\n", SSL_get_cipher(ssln));  
        ShowCerts(ssln);        // get any certs 
        SSL_write(ssln, msg, strlen(msg));   // encrypt & send message  
        bytes = SSL_read(ssln, bufnew, sizeof(bufnew)); // get reply & decrypt  
        bufnew[bytes] = 0;  
        printf("Received: \"%s\"\n", bufnew);  
        SSL_free(ssln);        // release connection state   
    }  
    close(server);         // close socket 
    SSL_CTX_free(ctxn);        // release context  
    return 0;  
}  

編譯時會給出錯誤

addr.sin_addr.s_addr = *(long*)(host->h_addr); 

我試圖查看hostent結構，但找不到任何解決方案。

Answer 1

這意味着編譯器不知道struct hostent的定義，因此您無法訪問它的任何成員。

您需要#include <netdb.h> ，請參閱文檔 。

Answer 2

您需要#include <netdb.h> ，其中包含hostent的定義。