pid_t and int

pid_t pid;

    //定义一个进程号类型的变量 pid

The type definition of the process number is often used when creating a process: pid_t. We all know that this type definition is actually an int type. But how is this definition defined in the header file of c under linux? Today I will post the previous process of finding this definition:

1. First, there are the following definitions in /usr/include/sys/types.h

#include <bits/types.h>
 
#ifndef __pid_t_defined
typedef __pid_t pid_t;
#define __pid_t_defined
#endif

You can see that pid_t is actually of type __pid_t.

2. You can see this definition in /usr/include/bits/types.h

#include <bits/typesizes.h>

#if __WORDSIZE == 32
        ......
 define __STD_TYPE        __extension__ typedef
＃elif __WORDSIZE == 64
          ......
#endif
        ......
__STD_TYPE __PID_T_TYPE __pid_t;    /* Type of process identifications.  */

It can be seen that __pid_t is defined as extension typedef __PID_T_TYPE.

3. You can see this definition in the file /usr/include/bits/typesizes.h (this file does not contain any header files):

#define __PID_T_TYPE        __S32_TYPE

It can be seen that __PID_T_TYPE is defined as __S32_TYPE.

4. In the file /usr/include/bits/types.h we finally found this definition:

#define    __S32_TYPE        int

From this we finally found the true definition of pid_t: in fact it is of type int.