APUE

Cause the not complement of the jekyll blog and not be able to the use of Markdown.

Take some of the review of today's summary of APUE ch-7.

1. exit ,_exit,_Exit 

use this functions to enter the OS

OS use the exec functions to enter the c start pro, then the main function ,then the user function.

2.return 0 , exit(0)

it depends on the compile .

today using :use return 0; to replace the effect of the exit(0);but Unix grep cant find the exit call;

ON the other hand：  use the exit(0) and void main（incorrect in programming design,int main() is defined in ISO C and  POSIX）

3.there is other functions library in red book C.

print the page and take notes some time.