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Wouldn't it make more sense (for example) for an int to always be 4 bytes?

How do I ensure my C programs are cross platform if variable sizes are implementation specific?

cat pants
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  • Related: [Exotic architectures the standard committee cares about](http://stackoverflow.com/q/6971886/2509) (yess, it's c++ but the issues are the same), [What platforms have something other than 8-bit char?](http://stackoverflow.com/q/2098149/2509), [What could C/C++ “lose” if they defined a standard ABI?](http://stackoverflow.com/q/2083060/2509) and others – dmckee --- ex-moderator kitten Nov 30 '11 at 03:43

3 Answers3

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The types' sizes aren't defined by c because c code needs to be able to compile on embedded systems as well as your average x86 processor and future processors.

You can include stdint.h and then use types like:

int32_t (32 bit integer type)

and

uint32_t (32 bit unsigned integer type)

Paul
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C is often used to write low-level code that's specific to the CPU architecture it runs on. The size of an int, or of a pointer type, is supposed to map to the native types supported by the processor. On a 32-bit CPU, 32-bit ints make sense, but they won't fit on the smaller CPUs which were common in the early 1970s, or on the microcomputers which followed a decade later. Nowadays, if your processor has native support for 64-bit integer types, why would you want to be limited to 32-bit ints?

Of course, this makes writing truly portable programs more challenging, as you've suggested. The best way to ensure that you don't build accidental dependencies on a particular architecture's types into your programs is to port them to a variety of architectures early on, and to build and test them on all those architectures often. Over time, you'll become familiar with the portability issues, and you'll tend to write your code more carefully. Becoming aware that not all processors have integer types the same width as their pointer types, or that not all computers use twos-complement arithmetic for signed integers, will help you to recognize these assumptions in your own code.

tuxedo
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You need to check the size of int in your implementation. Don't assume it is always 4 bytes. Use 

sizeof(int)
user1072577
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