How to execute some code before entering the main() routine in VC?

Question

I am reading Microsoft's CRT source code, and I can come up with the following code, where the function __initstdio1 will be executed before main() routine.

The question is, how to execute some code before entering the main() routine in VC (not VC++ code)?

#include <stdio.h>

#pragma section(".CRT$XIC",long,read)

int __cdecl __initstdio1(void);

#define _CRTALLOC(x) __declspec(allocate(x))

_CRTALLOC(".CRT$XIC") static pinit = __initstdio1;

int z = 1;

int __cdecl __initstdio1(void) {
    z = 10;
    return 0;
}

int main(void) {
    printf("Some code before main!\n");
    printf("z = %d\n", z);
    printf("End!\n");
    return 0;
}

The output will be:

Some code before main!
z = 10
End!

However, I am not able to understand the code.

I have done some google on .CRT$XIC but no luck is found. Can some expert explain above code segment to me, especially the followings:

1. What does this line _CRTALLOC(".CRT$XIC") static pinit = __initstdio1; mean? What is the significance of the variable pinit?
2. During compilation the compiler (cl.exe) throws a warning saying as below:

Microsoft (R) 32-bit C/C++ Optimizing Compiler Version 15.00.30729.01 for 80x86 Copyright (C) Microsoft Corporation. All rights reserved.

stdmacro.c
stdmacro.c(9) : warning C4047: 'initializing' : 'int' differs in levels of indirection from 'int (__
cdecl *)(void)'
Microsoft (R) Incremental Linker Version 9.00.30729.01
Copyright (C) Microsoft Corporation.  All rights reserved.

/out:stdmacro.exe
stdmacro.obj

What is the corrective action needs to be done to remove the warning message?

Thanks in advance.

Added:

I have modified the code and give type to pinit as _PIFV. Now the warning message is gone.

The new code is as follows:

#include <stdio.h>

#pragma section(".CRT$XIC1",long,read)

int __cdecl __initstdio1(void);

typedef int  (__cdecl *_PIFV)(void);

#define _CRTALLOC(x) __declspec(allocate(x))

_CRTALLOC(".CRT$XIC1") static _PIFV pinit1 = __initstdio1;

int z = 1;

int __cdecl __initstdio1(void) {
    z = 100;

    return 0;
}

int main(void) {
    printf("Some code before main!\n");
    printf("z = %d\n", z);
    printf("End!\n");
    return 0;
}

Answer 1

There's some information here (search for CRT). The significance of variable pinit is none, it's just a piece of data placed in the executable, where the runtime can find it. However, I would advise you to give it a type, like this:

_CRTALLOC(".CRT$XIC") static void (*pinit)()=...

The linker warning probably just warns you you have a function that has int return type, but doesn't return anything (probably you'd better change the return type to void).