C：使用UDP套接字寫文件時出錯

Question

我必須通過UDP 1024字節的文件（本例中爲txt文件）發送到服務器，並將這些字節寫入輸出文件。我收到此錯誤：

write(): bad address

我需要通過一個數據結構來傳遞字節，所以創建了一個名爲「PKT」與void *buf在那裏我可以寫字節結構。 這是我的示例程序。

客戶端：

#include <stdio.h> 
#include <stdlib.h> 
#include <fcntl.h> 
#include <sys/stat.h> 
#include <unistd.h> 
#include <string.h> 
#include <sys/socket.h> 
#include <arpa/inet.h> 

#define SERV_PORT   5197 
#define MAX_BLOCK_SIZE  1024 

struct pkt { 
    void *buf; 
    int num; 
}; 

int main(int argc, char *argv[]) { 

    if (argc != 3) { 
     fprintf(stderr, "Usage: %s <IP SERVER> <file>\n", argv[0]); 
     exit(EXIT_FAILURE); 
    } 

    int sockfd; 
    struct sockaddr_in addr; 
    int fd; 

    sockfd = socket(AF_INET, SOCK_DGRAM, 0); 
    if(sockfd < 0) 
    { 
     perror("socket()"); 
     exit(EXIT_FAILURE); 
    } 

    memset((void*)&addr, 0, sizeof(addr)); 
    addr.sin_family = AF_INET; 
    addr.sin_port = htons(SERV_PORT); 

    if (inet_pton(AF_INET, argv[1], &addr.sin_addr) <= 0) 
    { 
     perror("inet_pton()"); 
     exit(EXIT_FAILURE); 
    } 

    fd = open(argv[2], O_RDONLY); 
    if(fd == -1) 
    { 
     perror("open()"); 
     exit(EXIT_FAILURE); 
    } 
    //READ FILE 
    ssize_t n; 
    void *buf; 

    buf = alloca(MAX_BLOCK_SIZE); 
    n = read(fd, buf, MAX_BLOCK_SIZE); 
    if(n != MAX_BLOCK_SIZE) 
    { 
     perror("read()"); 
     exit(EXIT_FAILURE); 
    } 

    struct pkt packet; 
    packet.buf = buf; 
    packet.num = 0; 

    if(sendto(sockfd, &packet, sizeof(struct pkt), 0, (struct sockaddr*)&addr, sizeof(addr)) < 0) 
    { 
     perror("sendto()"); 
     exit(EXIT_FAILURE); 
    } 

    close(fd); 

    return EXIT_SUCCESS; 

} 

服務器側：

#include <stdio.h> 
#include <stdlib.h> 
#include <fcntl.h> 
#include <sys/stat.h> 
#include <unistd.h> 
#include <string.h> 
#include <sys/socket.h> 
#include <arpa/inet.h> 

#define SERV_PORT   5197 
#define MAX_BLOCK_SIZE  1024 

struct pkt { 
    void *buf; 
    int num; 
}; 

int main() { 
    int sockfd; 
    struct sockaddr_in addr; 
    socklen_t len; 
    int output; 

    output = open("test.txt", O_WRONLY|O_CREAT, 0664); 
    if(output == -1) 
    { 
     perror("open()"); 
     exit(EXIT_FAILURE); 
    } 

    sockfd = socket(AF_INET, SOCK_DGRAM, 0); 
    if(sockfd < 0) 
    { 
     perror("socket()"); 
     exit(EXIT_FAILURE); 
    } 

    memset((void*)&addr, 0, sizeof(addr)); 
    addr.sin_family = AF_INET; 
    addr.sin_addr.s_addr = htonl(INADDR_ANY); 
    addr.sin_port = htons(SERV_PORT); 

    if(bind(sockfd, (struct sockaddr*)&addr, sizeof(addr)) < 0) 
    { 
     perror("bind()"); 
     exit(EXIT_FAILURE); 
    } 

    while (1) { 
     len = sizeof(addr); 
     ssize_t n; 

     struct pkt packet; 
     n = recvfrom(sockfd, &packet, sizeof(struct pkt), 0, (struct sockaddr*)&addr, &len); 
     if(n < 0) 
     { 
      perror("recvfrom()"); 
      exit(EXIT_FAILURE); 
     } 

     printf("Packet number %d\n", packet.num); 

     void *buf = (packet.buf); 

     if (write(output, buf, MAX_BLOCK_SIZE) == -1) { 
      perror("write()"); 
      exit(EXIT_FAILURE); 

     } 
    } 

    return 0; 
} 

Answer 1

這一行：

packet.buf = buf; 

是與代碼的主要問題。

這一行所做的就是複製一個指向buf的指針。

所以當sendto（）被執行時，指針被髮送，而不是buf的內容。

建議：

取代：

struct pkt { 
    void *buf; 
    int num; 
}; 

與

struct pkt { 
    char buf[1024]; 
    int num; 
}; 

和替換這樣的：

packet.buf = buf; 

與

memcpy(packet.buf, buf, sizeof(packet.buf));