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bool isLittleEndian(){
int a = 0x12345678;

char *x = &a;

return x[0] == 0x78;

}

use-> uname -a | grep -q "x86" in /bin/sh

pointer size

define a union UNION { char a[4]; unint32 n;}; union UNION u; n = 0x12345678; if(u.a[0] == 0x12) return XXXXX-ENDIAN; if (u.a[0] == 0x78) return YYYYYY-ENDIAN;

int check_x86()
{
int a = 0x01020304;
char* b = (char*)&a;
return *b == 0x04;
}

#include<stdio.h>
#include<conio.h>
int main(int args,char *argv[],char* envp)
{
int i;
for(i=0;envp[i]!=NULL;i++)
{
printf("%s\n",envp[i]);
}
getch();
return 0;
}

There are compiler predefined macros that can do this check ,
#if defined(__sparc)
/* SPARC ---------------------------------------------------- */

#endif

#if defined(__x86_64__) || defined(_M_X64)
/* x86 64-bit ----------------------------------------------- */

#elif defined(__i386) || defined(_M_IX86)
/* x86 32-bit ----------------------------------------------- */

#endif