Keyword union, classic interview source code

 

Write a C function. If the processor is Big_endian, 0 is returned. If Little_endian is used, 1 is returned.

 

As we all know, the method for storing the number of CPUs in the Little-endian mode is from low bytes to high bytes, the Big-endian mode stores operands in bytes from high to low.

 

For example, the storage method of 16-bit 0x1234 in Little-endian mode CPU memory (assuming that it starts from address 0x4000) is:

Memory Address storage content

0X4000 0x34

0x4001 0x12

 

In Big-endian mode, the CPU memory is stored as follows:

Memory Address storage content

0X4000 0x12

0x4001 0x34

 

32-bit-width 0x12345678 storage method in the Little-endian mode CPU memory (assuming it starts from address 0x4000:

Memory Address storage content

0X4000 0x78

0x4001 0x56

0x4002 0x34

0x4003 0x12

 

In Big-endian mode, the CPU memory is stored as follows:

Memory Address storage content

0X4000 0x12

0x4001 0x34

0x4002 0x56

0x4003 0x78

 

 

The source code can be written as follows:

Int checkCPU ()

{

{

Union u

{

Int;

Char B;

} C;

C. a = 1;

Return (c. B = 1 );

}

}

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The storage order of union is that all members are stored from the low address. With this feature, the CPU can easily read and write the memory in the Little-endian or Big-endian mode.

 

This is easier and faster than any judgment statement!

 

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