socket() return -1 but errno 0
Solution 1
The first thing I would do is this:
sockfd = socket(AF_INET, SOCK_DGRAM, 0);
int tmp = errno;
RDF_LOG(kDEBUG, "sockfd %d ", sockfd);
if (sockfd < 0){
RDF_LOG(kERROR, "ERROR: %s , errno %d\n", strerror(tmp), tmp);
}
I have no idea what RDF_LOG
may be doing to the errno
variable and this will tell you whether it changes it or not.
Another thing to look for is that you have successfully performed your WSAStartup
. The following minimal program should hopefully show you how to do this, and provide a starting point for debugging:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <winsock2.h>
int main (void) {
WSADATA wsaData;
int listenFd;
if (WSAStartup(MAKEWORD(1,1), &wsaData) == SOCKET_ERROR) {
printf ("Error initialising WSA.\n");
return -1;
}
listenFd = socket (AF_INET, SOCK_STREAM, 0);
if (listenFd < 0) {
printf ("Error %d opening socket.\n", errno);
return -1;
}
return 0;
}
Solution 2
Because you are working with Windows sockets, you will need to use the WSAGetLastError() function to check the error code. Windows sockets functions do not set errno, which is why you are seeing errno with a value of 0.
This old MinGW wiki page has a list of differences between UNIX sockets and Windows sockets, mentioning the errno vs WSAGetLastError() difference in item 5: http://oldwiki.mingw.org/index.php/sockets
Solution 3
The function/macro RDF_LOG
is likely calling some other function in the C runtime library that is resetting errno
to 0. You need to capture the value of errno
immediately after socket
fails in order for it to be accurate.
twfx
Updated on October 25, 2020Comments
-
twfx over 3 years
I tried to create a UDP socket on mingw, but
socket()
returns-1
, with errno =0
. Strange. I have included winsock2.h. Initially I had compilation errorundefined reference to socket@12
, after setting-lws2_32
and-lwsock32
to Linker Settings of Code::Block, compilation success.sockfd = socket(AF_INET, SOCK_DGRAM, 0); RDF_LOG(kDEBUG, "sockfd %d ", sockfd); if (sockfd < 0){ RDF_LOG(kERROR, "ERROR: %s , errno %d\n", strerror(errno), errno); }
Result --> sockfd -1 ERROR: No error , errno 0
OK, I change RDF_LOG to fprintf instead.
int tmp = 0; sockfd = socket(AF_INET, SOCK_DGRAM, 0); tmp = errno; fprintf(stderr, "sockfd %d ", sockfd); if (sockfd < 0){ fprintf(stderr, "socket: %s , errno %d\n", strerror(tmp), tmp); }
The result returned is, still, --> sockfd -1 socket: No error , errno 0 Is it possible that mingw does not support errno??