CODEWITHSUNDEEP
cmacrosposix
AjanO
AjanO

Reputation: 473

Macro posix_c_source

I have the original code that is meant to compile in Windows and Linux using gcc. It works fine even under cygwin. Now, when I try to compile for iOS

echo $OSTYPE
darwin14

everything seems fine and a build is successfully obtained. However, when I tried to run the CUI app, a message Segmentation fault 11 is displayed.

After a couple of days searching on internet, by chance I found this link.

As a result, I made the following change in one of the *.c file

-#define _POSIX_C_SOURCE 199309
+#define _POSIX_C_SOURCE 199506

and the new build works fine. Although I am not a programmer, I am wondering what would be so significant different between these two macros? Could you comment on why such change becomes so significant.

Upvotes: 0

Views: 619

Answers (1)

Terrance Chen
Terrance Chen

Reputation: 11

though it is only 1 line of code,but it may make big difference,POSIX is a standard,it define the interface between OS and applications,and it has many different version(you can think it similar with a hardware USB standard , it has many version, like USB 1.0 and USB 2.0).

sometimes programmer can't determine which platform the program will be work on , it may run on Linux , may run on windows, maybe the system provide old standard interface, maybe a new one.

So , programmer add this kind of macros, write codes for many different interface,for example ,a source code like this:

#define WIN
#ifdef WIN
    <part 1:1000 lines of code>
#endif
#ifdef LINUX
    <part 2:1000 lines of code>
#endif 
    <1000 lines that not depend on system , can both run on Linux and Windows.>

the compiler will compile part 1(discard part 2), but when you change #define WIN to #define LINUX , it will contain part 2(and discard part 1) ! you may think you only changed 1 line , but the compiler may choose or discard thousands of lines (maybe even more ,maybe less, that depend on the code)

Upvotes: 1

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