Howard Shane Howard Shane - 5 months ago 24
Linux Question

Linux C: error of redefinition of in include headers

I have a project, which has below header include map:

main.c <- main.h <- tcphelper.h <- tcptest.h <- util.h
<- udptest.h <------------- util.h


In util.h, I defined a function prototype of struct cpu_usage:

void get_cpu_usage(struct cpu_usage *cu);


Now when I compile this project by GCC, I have this redefinition error. How do solve this problem?

thanks!

In file included from udptest.h:15:0,
from main.h:10,
from main.c:7:
util.h:27:8: error: redefinition of struct cpu_usage
struct cpu_usage{
^
In file included from tcptest.h:14:0,
from tcphelper.h:10,
from main.h:9,
from main.c:7:
util.h:27:8: note: originally defined here
struct cpu_usage{
^

Answer

You need to add Include guards to your header files to prevent including their contents multiple times. Example:

#ifndef UTIL_H_INCLUDED
#define UTIL_H_INCLUDED

/* header contents goes here */

#endif /* UTIL_H_INCLUDED */