“Socket operation on non-socket” error due to strange syntax
문제
I ran across the error Socket operation on non-socket
in some of my networking code when calling connect
and spent a lot of time trying to figure out what was causing it. I finally figured out that the following line of code was causing the problem:
if ((sockfd = socket( ai->ai_family, ai->ai_socktype, ai->ai_protocol) < 0)) {
See the problem? Here's what the line should look like:
if ((sockfd = socket( ai->ai_family, ai->ai_socktype, ai->ai_protocol)) < 0) {
What I don't understand is why the first, incorrect line doesn't produce a warning. To put it another way, shouldn't the general form:
if ( foo = bar() < baz ) do_something();
look odd to the compiler, especially running with g++ -Wall -Wextra
?
If not, shouldn't it at least show up as "bad style" to cppcheck, which I'm also running as part of my compile?
해결책
Actually, you don't get any warning because of the double parenthesis (
.
Try to remove one pair, and you'll get the warning back.
#include <iostream>
int foo()
{
return 2;
}
int main(int /*argc*/, char** /*argv*/)
{
int l;
if ((l = foo() < 3)) // Won't generate warning under gcc
{
}
if (l = foo() < 3) // will generate a warning "warning: suggest parentheses around assignment used as truth value"
{
}
return EXIT_SUCCESS;
}
To avoid such annoying mistakes/typos, I avoid assigning a value and testing it in the same statement. That's too much error prone imho.
다른 팁
That's one reason why I try not to do too much in one statement. Instead of
if ((sockfd = socket( ai->ai_family, ai->ai_socktype, ai->ai_protocol)) < 0) {
Why not:
sockfd = socket( ai->ai_family, ai->ai_socktype, ai->ai_protocol)
if(sockfd < 0) {