endianess and integer variable

In c I am little worried with the concept of endianess. Suppose I declare an integer (2 bytes) on a little endian machine as

int a = 1;

and it is stored as:

Address   value
1000       1
1001       0

On big开发者_JAVA技巧 endian it should be stored as vice-versa. Now if I do &a then I should get 1000 on on both machines.

If this is true then if I store int a=1 then I should get a=1 on little endian whereas 2^15 on big endian. Is this correct?

It should not matter to you how the data is represented as long as you don't transfer it between platforms (or access it through assembly code).

If you only use standard C - it's hidden from you and you shouldn't bother yourself with it. If you pass data around between unknown machines (for example you have a client and a server application that communicate through some network) - use hton and ntoh functions that convert from local to network and from network to local endianess, to avoid problems.

If you access memory directly, then the problem would not only be endian but also packing, so be careful with it.

In both little endian and big endian, the address of the "first" byte is returned. Here by "first" I mean 1000 in your example and not "first" in the sense of most-significant or least significant byte.

Now if I do &a then I should get 1000 on little endian and 1001 on big endian.

No; on both machines you will get the address 1000.

If this is true then if I store int a=1 then I should get a=1 on little endian whereas 2^15 on big endian. Is this correct?

No; because the preliminary condition is false. Also, if you assign 1 to a variable and then read the value back again, you get the result 1 back. Anything else would be a major cause of confusion. (There are occasions when this (reading back the stored value) is not guaranteed - for example, if multiple threads could be modifying the variable, or if it is an I/O register on an embedded system. However, you'd be aware of these if you needed to know about it.)

For the most part, you do not need to worry about endianness. There are a few places where you do. The socket networking functions are one such; writing binary data to a file which will be transferred between machines of different endianness is another. Pretty much all the rest of the time, you don't have to worry about it.

This is correct, but it's not only an issue in c, but any program that reads and writes binary data. If the data stays on a single computer, then it will be fine.

Also, if you are reading/writing from text files this won't be an issue.