我有两个文件。在accessories.c中，我定义了各种公共函数（比如logp-to-print log），并包含了各种公共库（比如sys/socket.h、string.h、stdio.h…）。现在，我计划的不是将sendfdsock.c, accessories.c包含在accessories.c中，或者先生成sendfdsock.c然后将其包含在acceessories.h中，而是先生成sendfdsock.c和sendfdsock.c and accessories.c的对象文件，然后在send中将它们链接在一起。执行此操作的命令（我没有生成任何直接链接的文件）：
gcc -c sendfdsock.c
gcc -c accessories.c
gcc -o send sendfdsock.o accessories.o
但是在第一个命令之后，我得到了一些错误和警告。这些错误的原因是
accessories.h需要一些函数和变量，这些函数和变量是在accessories.c中包含的gcc -c sendfdsock.c文件中定义的。这意味着gcc在生成对象文件时检查各种函数和变量的定义。但奇怪的是，我在sendfdsock.c中定义并在.h的第一行中使用的函数accessories.h没有错误或警告。也就是说，对于用户定义的函数没有错误/警告，而对于标准库则相反。为什么？
如何在gcc中进行编译？有没有什么好的资料可以简要地告诉我关于编译和链接的事情。
我还分享了这两个文件的代码（如果有人想看的话）：
logp()：#include <malloc.h>
#include <time.h>
#include <fcntl.h>
#include <unistd.h>
#include <stdio.h>
#include <errno.h>
#include <string.h>
#include <pthread.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netdb.h>
#include <error.h>
#include <signal.h>
#define PORT "4444" //port we are listening on
int sendall(int fd, char *buf, int *len)
{
int total = 0; // how many bytes we've sent
int bytesleft = *len; // how many we have left to send
int n;
while(total < *len) {
n = send(fd, buf+total, bytesleft, 0);
if (n == -1) { break; }
total += n;
bytesleft -= n;
}
*len = total; // return number actually sent here
return n==-1?-1:0; // return -1 on failure, 0 on success
}
int recvall(int fd, char *buf, int *len)
{
int total = 0; // how many bytes we've sent
int bytesleft = *len; // how many we have left to send
int n;
while(total < *len) {
n = recv(fd, buf+total, bytesleft, 0);
if (n == -1) { break; }
total += n;
bytesleft -= n;
}
*len = total; // return number actually sent here
return n==-1?-1:0; // return -1 on failure, 0 on success
}
void logp(int typ, char* msg) // typ --> type(category) of message [1-Normal Log, 2-Warning(any unexpected thing happened), 3-Error, 4-Debugging Log ]
{
int fd;
time_t now;
ssize_t wlength=0;
char * dat;
char * str;
int size = 45+strlen(msg);//14+24+5+sizeof msg+1
str= (char *) malloc(size);
time(&now);//system time in seconds
dat = ctime(&now); // converting seconds to date-time format
dat = strtok(dat,"\n");
//Appending type of log
switch(typ)
{
case 1:
strcpy(str,"__LOG__ | ");
strcat(str,dat);
break;
case 2:
strcpy(str,"__WARN__ | ");
strcat(str,dat);
break;
case 3:
strcpy(str,"__ERR__ | ");
strcat(str,dat);
break;
case 4:
strcpy(str,"__DEBUG__ | ");
strcat(str,dat);
break;
default:
strcpy(str,"__UNDEF__ | ");
strcat(str,dat);
break;
}
strcat(str," | ");
strcat(str,msg);//appending message
strcat(str,"\n");
fd = open("log", O_WRONLY | O_CREAT | O_APPEND, 0644); // should be opened somewhere else
if (fd == -1)
printf("Could not open log - %s\n",strerror(errno));
else
{//need to add lock to the file and printing error message
while ( wlength < strlen(str) )
{
wlength = write(fd, str,strlen(str));
if (wlength == -1)
{
printf("Error : writing log\n");
break;
}
}
}
}
void errorp(char *where, int boolean, int errn,char *what)
{
char errmsg[21+strlen(where)];
strcpy(errmsg,"Where - ");
strcat(errmsg,where);
strcat(errmsg," | Error - ");
if(boolean == 1)//we got error number
{
strcat(errmsg,strerror(errn));
//fprintf(stderr,"ERROR - In %s and error is %s\n",where ,strerror(errn));
logp(3,errmsg);
}
else if(boolean == 0)//we got a message
{
strcat(errmsg,what);
//fprintf(stderr,"ERROR - In %s and error is %s\n",where ,what);
logp(3,errmsg);
}
else//we got nothing
{
strcat(errmsg,"No Message");
//fprintf(stderr,"ERROR - In %s\n",where);
logp(3,errmsg);
}
}
accessories.c：#include <stropts.h>
#include <fcntl.h>
#include <sys/ioctl.h>
#include <sys/un.h>
#define CONTROLLEN CMSG_LEN(sizeof(int))
static struct cmsghdr *cmptr = NULL; /* malloc'ed first time */
int send_err(int fd, int errcode, const char *msg);
int send_fd(int fd, int fd_to_send);
int main(int argc, char const *argv[])
{
logp(1,"started");
int fd_to_send;
if((fd_to_send = open("vi",O_RDONLY)) < 0)
printf("vi open failed");
struct sockaddr_un address;
int socket_fd, nbytes;
char buffer[256];
socket_fd = socket(PF_UNIX, SOCK_STREAM, 0);
if(socket_fd < 0)
{
printf("socket() failed\n");
return 1;
}
/* start with a clean address structure */
memset(&address, 0, sizeof(struct sockaddr_un));
address.sun_family = AF_UNIX;
snprintf(address.sun_path, sizeof(address.sun_path)-1, "./demo_socket");
if(connect(socket_fd, (struct sockaddr *) &address, sizeof(struct sockaddr_un)) != 0)
{
printf("connect() failed\n");
return 1;
}
nbytes = snprintf(buffer, 256, "hello from a client");
// write(socket_fd, buffer, nbytes);
// nbytes = read(socket_fd, buffer, 256);
buffer[nbytes] = 0;
//printf("MESSAGE FROM SERVER: %s\n", buffer);
//sending the file descriptor
printf("From send_fd %d \n",send_fd(socket_fd,fd_to_send));
printf("Main end");
close(socket_fd);
exit(0);
}
int send_err(int fd, int errcode, const char *msg)
{
int n;
if ((n = strlen(msg)) > 0)
if (write(fd, msg, n) != n) /* send the error message */
return(-1);
if (errcode >= 0)
errcode = -1; /* must be negative */
if (send_fd(fd, errcode) < 0)
return(-1);
return(0);
}
int send_fd(int fd, int fd_to_send)
{
ssize_t temp;
struct iovec iov[1];
struct msghdr msg;
char buf[2]; /* send_fd()/recv_fd() 2-byte protocol */
iov[0].iov_base = buf;
iov[0].iov_len = 2;
msg.msg_iov = iov;
msg.msg_iovlen = 1;
msg.msg_name = NULL;
msg.msg_namelen = 0;
if (fd_to_send < 0) {
msg.msg_control = NULL;
msg.msg_controllen = 0;
buf[1] = -fd_to_send; /* nonzero status means error */
if (buf[1] == 0)
buf[1] = 1; /* -256, etc. would screw up protocol */
} else {
if (cmptr == NULL && (cmptr = malloc(CONTROLLEN)) == NULL)
return(-1);
cmptr->cmsg_level = SOL_SOCKET;
cmptr->cmsg_type = SCM_RIGHTS;
cmptr->cmsg_len = CONTROLLEN;
msg.msg_control = cmptr;
msg.msg_controllen = CONTROLLEN;
*(int *)CMSG_DATA(cmptr) = fd_to_send; /* the fd to pass */
buf[1] = 0; /* z ero status means OK */
}
buf[0] = 0; /* null byte flag to recv_fd() */
printf("before sendmsg \n");
temp = sendmsg(fd, &msg, 0);
if (temp != 2)
{
printf("inside sendmsg condition %d\n",temp);
return(-1);
}
printf("after sendmsg %d\n",temp);
return(0);
}
最佳答案
使用-Wall -pedantic编译并仔细检查：您可能会收到一个警告，告诉您隐式定义了int logp如果gcc找不到声明，它将执行此操作。
如果你不确定声明和定义的区别，开始阅读；-）