sizeof()在c中返回奇怪的值

Question

嗨,大家好我正在为一个赋值实现一个多协议服务器,问题是当我使用一个函数(对TCP很好用)和UDP时,它会返回一些奇怪的sizeof(rslt)值,这是打印sizeof的结果(RSLT),

0.000000

服务器

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

#define MAXLINE 100


struct equation {
    float a;
    char c;
    float b;
};

struct result {
    long double res;
};

int MAX (int a,int b){
    if (a>b) return a;
    return b;
}


int readn(int fd, void *vptr, size_t n)
{
    size_t  nleft;
    ssize_t nread;
    char   *ptr;
    ptr = vptr;
    nleft = n;
    while (nleft > 0) {
        if ( (nread = read(fd, ptr, nleft)) < 0) {
            if (errno == EINTR)
                nread = 0;      /* and call read() again */
            else
                return (-1);
        } else if (nread == 0)
            break;              /* EOF */

        nleft -= nread;
        ptr += nread;
    }
    return (n - nleft);         /* return >= 0 */
}


int writen(int fd, const void *vptr, size_t n)
{
    size_t nleft;
    ssize_t nwritten;
    const char *ptr;
    printf ("\nI'm In %Lf\n",n);
    ptr = vptr;
    nleft = n;
    printf ("%Lf NNNNN  %Lf SIZE %Lf \n",nleft,n,sizeof(*vptr));
    while (nleft > 0) {
        printf ("%Lf\n",nleft);
        fflush (stdout);
        if ( (nwritten = write(fd, ptr, nleft)) <= 0) {
            if (nwritten < 0 && errno == EINTR)
                nwritten = 0;   /* and call write() again */
            else
                return (-1);    /* error */
        }

        nleft -= nwritten;
        ptr += nwritten;
    }
    printf ("\n 5alawees \n");
// printf ("\n%s\n",vptr);
//    ffulsh (stdout);
    return (n);
}

void HandleClient(int comm_fd);
void Die (const char * msg)
{
    perror(msg);
    exit(1);
}

int passiveUDP (short port){
    struct sockaddr_in servaddr;
    int listen_fd;
    if ((listen_fd = socket(AF_INET, SOCK_DGRAM, 0)) < 0)
    {
        Die("Falied to create socket");
    };

    //printf ("%d" ,listen_fd);
    memset( &servaddr,0, sizeof(servaddr));

    servaddr.sin_family = AF_INET;
    servaddr.sin_addr.s_addr = htons(INADDR_ANY);
    servaddr.sin_port = htons(port);

    if (bind(listen_fd, (struct sockaddr *) &servaddr, sizeof(servaddr))<0)
    {
        Die("Failed to bind socket to address");
    }
    return listen_fd;
}

int passiveTCP (short port){
    struct sockaddr_in servaddr;
    int listen_fd;
    if ((listen_fd = socket(AF_INET, SOCK_STREAM, 0)) < 0)
    {
        Die("Falied to create socket");
    };

    memset( &servaddr,0, sizeof(servaddr));

    servaddr.sin_family = AF_INET;
    servaddr.sin_addr.s_addr = htons(INADDR_ANY);
    servaddr.sin_port = htons(port);

    if (bind(listen_fd, (struct sockaddr *) &servaddr, sizeof(servaddr))<0)
    {
        Die("Failed to bind socket to address");
    }

    if (listen(listen_fd, 10) < 0)
    {
        Die("Failed to listen on server socket");
    }
    return listen_fd;
}

int main(int argc, char * argv[])
{
    if (argc != 2) {
        fprintf(stderr, "USAGE: ./HelloITServer <port>\n");
        exit(1);
    }
    char str[100];
    int listen_fd, comm_fd;
    int    usock = passiveUDP (atoi (argv[1]));               /* UDP socket  */

    int    tsock = passiveTCP (atoi (argv[1]));           /* TCP master socket  */
    int    nfds;
    fd_set rfds;                 /* readable file descriptors */
    struct sockaddr_in fsin;     /* the request from address */

    nfds = MAX(tsock, usock) + 1;
    FD_ZERO(&rfds);
    while (1) {
        FD_SET(tsock, &rfds);
        FD_SET(usock, &rfds);
        printf ("HELLO");
        if(select(nfds, &rfds, NULL, NULL, NULL) < 0){
            printf("select error: %d \n",errno);
            exit (1);
        }
        if(FD_ISSET(tsock, &rfds))
        {
            /* TCP slave socket */
            printf ("Hello TCP");
            int ssock;
            //int alen = sizeof(fsin);
            ssock = accept(tsock, (struct sockaddr *) NULL, NULL);
            if(ssock < 0)
                Die("accept failed: jkjkjkjkjkj \n");
            HandleClient (ssock);
            close (ssock);
        }
        if(FD_ISSET(usock, &rfds))
        {
            printf ("Hello UDP");
            HandleClient (usock);
        }
    }

}
void HandleClient(int comm_fd)
{
    struct equation eq;
    struct result rslt;
    bzero (&eq,sizeof (eq));
    bzero (&rslt, sizeof (rslt));
    if ((readn (comm_fd, &eq, sizeof(eq))) == 0){
        Die("Failed to receive from client");
    }
    printf ("\n%Lf  %Lf\n",sizeof (struct result),sizeof (rslt));
    printf ("reciveed %f %c %f",eq.a,eq.c,eq.b);
    switch (eq.c) {
        case '+':
            rslt.res = eq.a+eq.b;
            break;
        case '-':
            rslt.res = eq.a-eq.b;
            break;
        case '*':
            rslt.res = eq.a*eq.b;
            break;
        case '/':
            rslt.res = eq.a/eq.b;
            break;
        case '%':
            rslt.res = (int)eq.a% (int)eq.b;
            break;
        default:
            break;
    }
    printf ("\n%Lf\n",sizeof(rslt));
    printf ("\n%Lf\n",sizeof(rslt));
    printf ("\n%Lf\n",sizeof(rslt));

    writen (comm_fd, &rslt, sizeof (rslt));
    //close (comm_fd);
}

客户(以防万一你需要它)

#include <sys/types.h>
#include <sys/socket.h>
#include <netdb.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include<unistd.h>
#include <float.h>
#include <errno.h>

struct equation {
    float a;
    char c;
    float b;
};

struct result {
    long double res;
};

int readn(int fd, void *vptr, size_t n)
{
    size_t  nleft;
    ssize_t nread;
    char   *ptr;
    ptr = vptr;
    nleft = n;
    while (nleft > 0) {
        if ( (nread = read(fd, ptr, nleft)) < 0) {
            if (errno == EINTR)
                nread = 0;      /* and call read() again */
            else
                return (-1);
        } else if (nread == 0)
            break;              /* EOF */

        nleft -= nread;
        ptr += nread;
    }
    return (n - nleft);         /* return >= 0 */
}

int writen(int fd, const void *vptr, size_t n)
{
    size_t nleft;
    ssize_t nwritten;
    const char *ptr;

    ptr = vptr;
    nleft = n;
    while (nleft > 0) {
        if ( (nwritten = write(fd, ptr, nleft)) <= 0) {
            if (nwritten < 0 && errno == EINTR)
                nwritten = 0;   /* and call write() again */
            else
                return (-1);    /* error */
        }

        nleft -= nwritten;
        ptr += nwritten;
    }
    return (n);
}

int main(int argc,char *argv[])
{
    int sockfd,n;
    char sendline[100];
    char recvline[100];
    struct sockaddr_in servaddr;
    if (argc != 3) {
        fprintf(stderr, "USAGE: ./HelloClient <server_ip> <port>\n");
        exit(1);
    }

    sockfd=socket(AF_INET,SOCK_DGRAM,0);
    bzero(&servaddr,sizeof servaddr);

    servaddr.sin_family=AF_INET;
    servaddr.sin_port= htons(atoi(argv[2]));

    inet_pton(AF_INET,argv[1],&(servaddr.sin_addr));

    connect(sockfd,(struct sockaddr *)&servaddr,sizeof(servaddr));
    struct result rslt;
    struct equation eq;
    //while(1)
    //{
    printf ("Accepted values by the program, from %f to %f\n", FLT_MIN, FLT_MAX);
    printf ("\n possible operations are addition, substraction, division, multiplication and modulo with operators : +,-,*,/,% respectivly\n");
    printf ("\nPlease enter the equation in this form only : \"5.0 + 2.0\" with a single space\n");
    scanf ("%f %c %f", &eq.a,&eq.c,&eq.b);
    if (eq.c!='+' && eq.c!='-' && eq.c!='*' && eq.c!='/' && eq.c!='%'){
        printf ("\n possible operations are addition, substraction, division, multiplication and modulo with operators : +,-,*,/,% respectivly\n");
        exit (1);
    }
    if (eq.c== '%'){
        if (!(eq.a == (float) ((int) eq.a) && eq.b == (float) ((int) eq.b))){
            printf ("Only integer values are accepted with the % operation, please rerun the program\n");
            exit (1);
        }
    }
    //bzero( &eq, sizeof(eq));
    bzero( &rslt, sizeof(rslt) );
    //fgets(sendline,100,stdin); /*stdin = 0 , for standard input */
    writen (sockfd, &eq, sizeof(eq));

    readn (sockfd, &rslt, sizeof(rslt));
    printf("%Lf\n thank you for using this marvelous calculator!\n",rslt.res);
    bzero( &eq, sizeof(eq));
    exit (1);
    //}
}

Answer 1

sizeof() 返回未指定类型的无符号整数值.

格式规范%Lf需要一个long double参数.

尝试:

printf ("\n%u\n",(unsigned int) sizeof(rslt));

或者,如果你要打印的内容的rslt:

printf ("\n%Lf\n",rslt.res);

请注意,当我printf("%Lf\n", sizeof(rslt));使用gcc 4.6.3 编译代码时,我会收到以下警告(请注意,没有"增强警告"选项,例如-Wall必要的):

so-test.c:13:33: warning: format ‘%Lf’ expects argument of type ‘long double’, but argument 2 has type ‘long unsigned int’ [-Wformat]

并非所有编译器都如此有用,但如果您使用GCC,则应注意警告.

Answer 2

问题代码中有几个地方试图将sizeof()的结果'printf()'作为'long double'值:

printf ("\n%Lf  %Lf\n",sizeof (struct result),sizeof (rslt));
...
printf ("\n%Lf\n",sizeof(rslt));
printf ("\n%Lf\n",sizeof(rslt));
printf ("\n%Lf\n",sizeof(rslt));

而不是使用'%Lf',使用"%zu"打印'sizeof()'返回的'size_t'值.

(使用"%zd"打印'ssize_t'值)