從緩存中獲取緩衝

Question

我正在嘗試編寫通過UDP進行通信的tic-tack-toe遊戲。 現在我有一些代碼：

int recv_txt(int sock, struct sockaddr_in *incoming_addr) 
{ 
    char bud[MAX_LENGTH]; 
    unsigned int incoming_add_len; 
    incoming_add_len = sizeof(*incoming_addr); 
    if(recvfrom(sock, &buf, MAX_LENGTH, 0 (struct sockaddr*)incoming_addr, &incoming_addr_len) < 0) 
    { 
     return 0; 
    } 
    printf("received %s", buf); 
    return 1; 
} 

int main(int argv, char **argc) 
{ 
    /** some code to create socket etc */ 
    struct sockaddr_in incoming_addr; 
    for(;;) 
    { 
     recv_txt(sock, &incoming_addr); 

     //here I would like to create new thread, which will process the buffer from recv_txt and send response; 
    } 
} 

，現在我需要從recv_txt得到緩衝，把它裏面的結構是這樣的：

struct M_s 
{ 
    struct sockaddr_in address; 
    char[MAX_LENGTH] buffer; 
} 

，並把它傳遞給新的線程。但我無法從recv_txt獲得緩衝區。我很新的C，現在我不能使用指針非常好。

感謝您的任何建議。

編輯

我試圖通過Frankie_c提供的解決方案，但我有問題，現在printf。 當我嘗試在main：

LP_ARGS_STRUCT args = recv_txt(sock) 
printf("data from: %s", inet_ntoa(args->address.sin_adrr)) 

我沒有得到任何打印到控制檯或遇到錯誤信息。

EDIT2 - 全碼

#include <stdio.h> 
#include <unistd.h> 
#include <stdlib.h> 
#include <string.h> 

#include <sys/socket.h> 
#include <netinet/in.h> 
#include <arpa/inet.h> 

#include <pthread.h> 

#define SRV_PORT   23456 
#define MAX_TXT_LENGTH  1000 
#define MAX_ROOMS   1 

int sock; 

typedef struct args_s 
{ 
    struct sockaddr_in address; 
    char buffer[MAX_TXT_LENGTH]; 
} ARGS_STRUCT, *LP_ARGS_STRUCT; 
//typedef struct args_s args; 


LP_ARGS_STRUCT recv_txt(int sock) 
{ 
    LP_ARGS_STRUCT args = malloc(sizeof(ARGS_STRUCT)); 

    //memory error 
    if(!args) 
    { 
     return 1; 
    } 

    unsigned int incoming_addr_len = sizeof(args->address); 

    //incoming_addr_len = sizeof(*incoming_addr); 
    if (recvfrom(sock, &args->buffer, MAX_TXT_LENGTH, 0, 
        (struct sockaddr*)&args->address, &incoming_addr_len) < 0) 
    { 
     free(args); 
     return NULL; 
    } 
    printf("received: %s %s\n", args->buffer, inet_ntoa(args->address.sin_addr)); 
    return 1; 
} 

int main(int argv, char **argc) 
{ 
    int i = 0; 

    int optval; 
    struct sockaddr_in addr, incoming_addr; 
    char buffer[MAX_TXT_LENGTH]; 

    /* create socket */ 
    sock = socket(PF_INET, SOCK_DGRAM, IPPROTO_UDP); 
    if (sock < 0) 
    { 
     err("socket()"); 
    } 

    /* set reusable flag */ 
    optval = 1; 
    setsockopt(sock, SOL_SOCKET, SO_REUSEADDR, &optval, sizeof(optval)); 

    /* prepare inet address */ 
    memset(&addr, 0, sizeof(addr)); 
    addr.sin_family = AF_INET; 
    addr.sin_port = htons(SRV_PORT); 
    addr.sin_addr.s_addr = htonl(INADDR_ANY); /* listen on all interfaces */ 
    if (bind(sock, (struct sockaddr*)&addr, sizeof(addr)) < 0) 
    { 
     err("bind"); 
    } 


    for(;;) 
    { 


     LP_ARGS_STRUCT args = recv_txt(sock); 
     if(!args) continue; 
     printf("%s\n", args->buffer); 

    } 

    return 0; 
} 

和接收數據包後，我得到：

received: Hello 192.168.56.1 
Segmentation fault (code dumped) 

Process returned 139 (0x8B) 

Answer 1

對於原來的問題試試這個：

typedef struct M_s 
{ 
    struct sockaddr_in address; 
    char[MAX_LENGTH] buffer; 
} M_STRUCT, *LP_M_STRUCT; //Create a typedef for struct 

//Modify your function to return a structure pointer and having just socket as par... 
LP_M_STRUCT recv_txt(int sock) 
{ 
    LP_M_STRUCT pMs = malloc(sizeof(M_STRUCT)); 
    if (!pMs) 
    { 
     //Handle memory error here! 
     return NULL; 
    } 

    unsigned int incoming_add_len = sizeof(pMs->incoming_addr); 

    if (recvfrom(sock, &pMs->buffer, MAX_LENGTH, 0, (struct sockaddr *)&pMs->incoming_addr, &incoming_addr_len) < 0) 
    { 
     free(pMs);  //Release memory 
     return NULL; //Return nothing... 
    } 

    //If we are here we were successfull. 
    //The structure pMs holds all data we need... so give it to caller... 
    printf("From %s received %s", inet_ntoa(pMs->address.sin_addr), pMs->buffer); 
    return pMs; 
} 

int main(int argv, char **argc) 
{ 
    /** some code to create socket etc */ 

    for (;;) 
    { 
     LP_M_STRUCT pMs = recv_txt(sock); 
     if (!pMs) //Check if we get a sign of life on UDP... 
      continue; //No continue to wait for ... 

     //We print values again to check that it is ok... 
     printf("From %s received %s", inet_ntoa(pMs->address.sin_addr), pMs->buffer); 

     //here create new thread to process the buffer from recv_txt and send response; 
     //The new thread code have to release structure memory when done!!! 
    } 
} 

編輯：你的問題是你不返回分配結構成功時，並且在失敗時不返回NULL。請參閱：

LP_ARGS_STRUCT recv_txt(int sock) 
{ 
    LP_ARGS_STRUCT args = malloc(sizeof(ARGS_STRUCT)); 

    //memory error 
    if(!args) 
    { 
     //return 1; !!!WRONG!!! 
     return NULL; 
    } 

    unsigned int incoming_addr_len = sizeof(args->address); 

    //incoming_addr_len = sizeof(*incoming_addr); 
    if (recvfrom(sock, &args->buffer, MAX_TXT_LENGTH, 0, 
        (struct sockaddr*)&args->address, &incoming_addr_len) < 0) 
    { 
     free(args); 
     return NULL; 
    } 
    printf("received: %s %s\n", args->buffer, inet_ntoa(args->address.sin_addr)); 
    //return 1; WRONG! You have to return the allocated struct 
    return args; 
}