function 'rand_r' 的隐式声明

Question

I know there are a lot of questions with a similar title, but so far I have not found one that could solve my situation.

When making the file, I got prompted with

warning: implicit declaration of function ‘rand_r’ [-Wimplicit-function-declaration]

But I have already included stdlib.h and unistd.h , why is it still happening? Is it because of the makefile?

I am running this on Linux and my makefile is roughly as follows:

prog: prog.o
    gcc -g -o $@ $^ -lpthread

%.o:%.c *.h
    gcc -ansi -pedantic -Wimplicit-function-declaration -Wreturn-type -g -c $< -o $@

Thank you

Answer 1

rand_r() manpage reads:

The functions rand() and srand() conform to SVr4, 4.3BSD, C89, C99, POSIX.1-2001. The function rand_r() is from POSIX.1-2001. POSIX.1-2008 marks rand_r() as obsolete.

Your compilation options specify -ansi (C89/C90) thus limiting you to rand() and srand() .