Question

我在实现C UDP套接字程序时遇到问题。下面的代码对于任何少于56个字符的输入都可以完美地工作，但是如果我输入的字符少于或等于56个字符，sendto会抱怨我给了它无效的参数（错误代码22）。例如，这将正确发送：

 ./talkerDemo localhost qqqqqwwwwweeeeeqqqqqwwwwweeeeeqqqqqwwwwweeeeeqqqqqwwwww

但这不会：

 ./talkerDemo localhost qqqqqwwwwweeeeeqqqqqwwwwweeeeeqqqqqwwwwweeeeeqqqqqwwwwwH

有什么作用？

/*
** talker.c
** Adapted from http://beej.us/guide/bgnet/html/single/bgnet.html#datagram
*/

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

#define SERVERPORT "4242"    // the port users will be connecting to

int main(int argc, char *argv[])
{
    int sockfd;
    struct addrinfo hints, *servinfo, *p;
    int rv;
    int numbytes;

    if (argc != 3) {
        fprintf(stderr,"usage: talker hostname message\n");
        exit(1);
    }

    memset(&hints, 0, sizeof hints);
    hints.ai_family = AF_UNSPEC;
    hints.ai_socktype = SOCK_DGRAM;

    if ((rv = getaddrinfo(argv[1], SERVERPORT, &hints, &servinfo)) != 0) {
        fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(rv));
        return 1;
    }

    // loop through all the results and make a socket
    for(p = servinfo; p != NULL; p = p->ai_next) {
        if ((sockfd = socket(p->ai_family, p->ai_socktype,
                p->ai_protocol)) == -1) {
            perror("talker: socket");
            continue;
        }

        break;
    }

    if (p == NULL) {
        fprintf(stderr, "talker: failed to create socket\n");
        return 2;
    }



//============================================================
// !!!!!!! Eror occurs here:   
    if ((numbytes = sendto(sockfd, argv[2], strlen(argv[2]), 0,
             p->ai_addr, p->ai_addrlen)) == -1) {
        perror("talker: sendto");
        exit(1);
    }
//============================================================

    freeaddrinfo(servinfo);

    printf("talker: sent %d bytes to %s\n", numbytes, argv[1]);
    close(sockfd);

    return 0;
}

编辑

这是我实际运行的代码版本。在发布问题之前，我已经回到原始问题（上图），以查看问题是否也发生在该实现上-好像是这样。但是事实证明我很胖，并且使用了错误的二进制文件... derp

/*
** UDPTalker.hpp -- a datagram sockets "server"
** Adapted from http://beej.us/guide/bgnet/html/single/bgnet.html#datagram
*/

#ifndef UDPTALKER_H
#define UDPTALKER_H

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

#include <iostream>
#include <string>


#define UDPT_DEFAULT_PORT "4243"
#define UDPT_DEFAULT_HOST "localhost"

#define UDPT_MAXBUFLEN 2048


class UDPTalker {
    int sockfd;
    struct addrinfo hints, *servinfo, *p;
    int rv;
    int numbytes;

    std::string host;
    std::string port;

    public:
        //! Takes target hostname/ip and port as arguments. Defaults: ("localhost", "4243")
        UDPTalker(std::string host = UDPT_DEFAULT_HOST, std::string port = UDPT_DEFAULT_PORT);

        ~UDPTalker();

        void send(std::string msg);
};

#endif // UDPTALKER_H

以下是相应的.cpp：

// File UDPTalker.cpp

#include "UDPTalker.hpp"

UDPTalker::UDPTalker(std::string h, std::string port) : host(h), port(port) {
    memset(&hints, 0, sizeof hints);
    hints.ai_family = AF_UNSPEC;
    hints.ai_socktype = SOCK_DGRAM;

    if ((rv = getaddrinfo(host.c_str(), port.c_str(), &hints, &servinfo)) != 0) {
        throw std::runtime_error(std::string("getaddrinfo: ").append(gai_strerror(rv)));
    }

    // loop through all the results and make a socket
    for(p = servinfo; p != NULL; p = p->ai_next) {
        if ((sockfd = socket(p->ai_family, p->ai_socktype,
                p->ai_protocol)) == -1) {
            perror("talker: socket");
            continue;
        }

        break;
    }

    freeaddrinfo(servinfo);

    if (p == NULL) {
        throw std::runtime_error("talker: failed to create socket\n");
    }
}

UDPTalker::~UDPTalker() {
    close(sockfd);
}

void UDPTalker::send(std::string msg) {

    if ((numbytes = sendto(sockfd, msg.c_str(), msg.size(), 0,
             p->ai_addr, p->ai_addrlen)) == -1) {
        perror("talker: sendto! ");
    }

    // printf("talker: sent %d bytes to %s\n", numbytes, host.c_str());
}

Answer 1

servinfo释放p使用的内存。这意味着指针sendto现在指向空内存，因此当它传递给send时，它可能具有无效的内容。我的猜测是，由于某种原因，在调用类的freeaddrinfo(servinfo);方法时，输入字符串中的多余字节正在“翻转”该内存位置。解决方法是将UDPTalker::UDPTalker(std::string h, std::string port) : host(h), port(port) { memset(&hints, 0, sizeof hints); hints.ai_family = AF_UNSPEC; hints.ai_socktype = SOCK_DGRAM; if ((rv = getaddrinfo(host.c_str(), port.c_str(), &hints, &servinfo)) != 0) { throw std::runtime_error(std::string("getaddrinfo: ").append(gai_strerror(rv))); } // loop through all the results and make a socket for(p = servinfo; p != NULL; p = p->ai_next) { if ((sockfd = socket(p->ai_family, p->ai_socktype, p->ai_protocol)) == -1) { perror("talker: socket"); continue; } break; } if (p == NULL) { throw std::runtime_error("talker: failed to create socket\n"); } } UDPTalker::~UDPTalker() { freeaddrinfo(servinfo); close(sockfd); }从构造函数移至析构函数：

countL = 0
countR = 0
runL = True
runR = True
running = True
speed = 60


try:

  lastValidL = 2
  lastValidR = 2
  lastL = pi2go.irLeftLine()
  lastR = pi2go.irRightLine()
  while True:
    if pi2go.getDistance() >=8:
      while pi2go.getDistance() >=8:
        if countR > countL:
          pi2go.turnForward(90,85)
        if countR < countL:
          pi2go.turnForward(85,90)
        if countR == countL:
          pi2go.turnForward(85,90)
        val = pi2go.irLeftLine()
        if val == lastL and val != lastValidL:
          countL +=1
          lastValidL = val
        lastL = val
        print "L:", countL
        val = pi2go.irRightLine()
        if val == lastR and val != lastValidR:
          countR += 1
          lastValidR = val
        lastR = val
        print "R:", countR
#heres the function I want.
        oldL = countL +
        print oldL
        if True:
          if oldL == countL:
            time.sleep(5) 
            #if oldL has still the same value as count L
            if oldL == countL 
              pi2go.stepReverse(80,20)

与输入有关的错误：sendto（）错误代码22（无效参数）取决于输入大小

编辑

1 个答案: