Use C language program to determine the size of the end pattern

1. In big-end mode, the low value of data is stored in the high address of memory, while the high value of data is stored in the low address of memory; The small-end pattern is reversed

  2. Why are there different ends?

  Because in a computer system, storage is in bytes, each address cell corresponds to a byte, a byte =8bit. In C, in addition to 8bit char, there are 16bit short and 32bit long (depending on the compiler). For processors with bits greater than 8 bits, such as 16-bit or 32-bit processors, how to arrange the storage of multiple bytes because the register width is greater than one byte

3. Respective advantages:

Small - end mode: cast data does not need to adjust the byte content, 1, 2, 4 bytes stored in the same way.

Big-end mode: the symbol bit is fixed as the first byte, easy to determine the positive and negative.

4. The commonly used X86 structure is the small-end mode, while KEIL C51 is the big-end mode. A lot of ARM, DSP is small - end mode.

5.C language determines the size of the end pattern

Method one:

void IsBigEndian()
{
 short int a = 0x1122;//Hexadecimal, one number has four digits
 char b =  *(char *)&a;  //By casting short(2 bytes) into a char single byte, b points to the starting byte of a (low byte)
 if( b == 0x11)//Low byte save is the high byte of data
 {
  //Big end mode
 }
 else
 {
  //Small end mode
 }
}

Method 2:

void IsBigEndian()//How it works: the storage order for a union is that all members start at a low address, and all members share storage space
{
 union temp
 {
  short int a;
  char b;
 }temp;
 temp.a = 0x1234;
 if( temp.b == 0x12 )//Low byte save is the high byte of data
 {
  //Big end mode
 }
 else
 {
  //Small end mode
 }
}

On my machine, I verified the small-end mode

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