Dealing with dynamic integer types in C?

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+2 Q:

Dealing with dynamic integer types in C?

I'm developing a Python module in C that parses a very efficient protocol which uses dynamic integer sizes. Integers sent using this protocol can range in size from the equivalent of C's 'short' to a 'long long.'

The protocol has a byte that specifies the type of variable being sent (from short to long long), but I'm not sure how to deal with this in code. Right now, I'm setting up a void pointer and allocating memory in the size of the value being sent -- then using atoi, atol, and atoll to set that pointer. The problem is, I need to be able to access that value, and am unable to do so without it being cast later.

What are some good ways to handle this issue?

+4 A:

Either always store it in a long long locally, or put it in a struct composed of a flag for the size and a union of all the possible types.

Ignacio Vazquez-Abrams 2010-02-22 03:46:13

I'm a little confused about how to use a struct/union for that.. Have a quick example?

2010-02-22 03:50:30

`typdef struct {`` char flag;`` union {`` unsigned char ubyte;`` unsigned long ulong;`` unsigned long long ulonglong;`` }``} mystruct`

Ignacio Vazquez-Abrams 2010-02-22 03:54:50

Then you'd just always cast the union as a long long when you're accessing it in code? Or do you have to switch off of that flag and cast accordingly?

2010-02-22 03:57:00

You switch off `.flag` and read the appropriate member (`.ubyte`, `.ulong`, etc.).

Ignacio Vazquez-Abrams 2010-02-22 03:58:32

Thanks a lot! Gonna stick with using long longs locally.

2010-02-22 04:05:04

The first part of this answer, always using a long long, is going to be easier for you without any loss, compared to the second part of using a union.

Roger Pate 2010-02-22 04:34:45

That's what I figured -- just was trying to decide if it was efficient to do so -- doing it with a union will definitely be a pain if I have to switch off of that flag each time.

2010-02-22 18:40:23

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Dealing with dynamic integer types in C?

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