Ubuntu系统中具有不同内容的相同名称标头

Question

I have two c++ projects in my Eclipse that uses same function gettimeofday() . First project compiles fine while other reports error

error: ‘gettimeofday’ was not declared in this scope

By presing F3 on function name I found that in first project case I was navigated to /usr/include/86_64-linux-gnu/sys/time.h . Second project also has #include <time.h> , but F3 navigates to sys/time.h , which has no 'gettimeofday' function.

Why same #include <time.h> navigates to different folders? Why Linux has two same names includes at all? Why both includes #include <time.h> are different?

UPD

I found that /sys/timeb.h has inclusion #include <time.h> which navigates to /usr/lib/time.h . I was expecting /sys/timeb.h will include /sys/timeb.h. How Eclipse and GCC decides to go /sys/timeb.h. How Eclipse and GCC decides to go /usr/lib/time.h or /sys/time.h` ?

Why "professional" /sys/timeb.h leaves ambiguity in code just by making #include <time.h> instead defining more exact path? I suppose <time.h> might point to both - <sys/time.h> and C <time.h>

Answer 1

On Linux, the function int gettimeofday(struct timeval *tv, struct timezone *tz); is defined in #include <sys/time.h> . When using it in your code you should include it exactly like that. The other time.h is the standard C library that contains time structures and functions such as time_t and mktime . When you are using this file in a C++ program you should include it as #include <ctime> which should help you avoid this type of error in the future.