Get sigaction structure

Question

Trying to build paho_c_pub.c with help of Visual Studio 2019 on my Raspberry Pi machine connected via ssh. Code uses structure sigaction from <signal.h> that is not visible by compiler:

Error       invalid application of ‘sizeof’ to incomplete type ‘struct sigaction’
Error       storage size of ‘sa’ isn’t known

I have no such errors when I build code in console:

cc paho_c_sub.c pubsub_opts.c -o paho_c_sub -l paho-mqtt3as

What is wrong with Visual Studio C project configuration?

Answer 1

Your code needs to have

#define  _POSIX_C_SOURCE  200809L

before the

#include <signal.h>

as described in man 3 sigaction, in the Feature Test Macro requirements for glibc part of the Synopsis.

Whenever you compile code, you should enable warnings (-Wall).

Without the above definition, the sigaction() function is not exposed, and your compiler uses the standard C rules on determining exactly what to pass to it. It happens to work, because it takes an int and two pointers as parameters; but when warnings are enabled (and especially when warnings are treated as errors, as in your Visual Studio 2019 environment), the compiler points out this issue. Adding the #define should make both work correctly, without relying on happenstance.