C language large and small end mode judgment function

It's me DEV C++ The mode judgment function of the large and small ends written in , After operation a Output 1, It should be the big end mode , But the specific judgment principle is not very clear , We also need your guidance . Remember the usual x86 It's small end mode

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#include "stdio.h" 

int CheckSystem()
{
    
	union check
	{
    
		int i;
		char ch;
	}c;
	c.i=1;
	return(c.ch==1);
}

void main()
{
    
	int a=0;
	a=CheckSystem();
	
	printf("%d\n",a);
}