Compile time checking existence of stdint.h

Question

I'm working with legacy embedded C code which defines the types uint8_t, uint16_t and uint32_t in a header file using the typedef keyword.

For discussion, let us say the file typedefs.h contains these definitions.

In my new C source module, I include stdint.h. I also include other header files which include typedefs.h somewhere in the hierarchy. As expected, the compiler complains about multiple defined symbols.

I would like to modify the legacy file typedefs.h so that it only declares the uint*_t types if either stdint.h is not included or better if the uint*_t types are not defined.

My understanding is that #ifndef cannot be used since typedef is not a preprocessor directive.

So how do I tell the compiler to not define the uint*_t if they already exist (or if the stdint.h is already included)?

Note: this would be easy if the C specification defined standard include guard definitions for the header files.

FWIW, I am using Green Hills compiler, 4.24, for an ARM9 processor.

Coltish

Answer 1

Just fix the legacy header to always include stdint.h to get these types, remove the duplicate definitions, and provide a drop-in file stdint.h for broken systems that lack it.

Argybargy

Answer 2

I beleive that the stdint.h should also be defining a macro for the limits of the types that it defines. You should be able to test for those using a #ifdef and the like.

#ifndef UINT32_MAX
  typdef ... uint32_t;
  #define UINT32_MAX ...
  ...
#endif

Edit: Originally used UINT32_MIN, but as Jens Gustedt poited out this is the one combination of signed/unsigned and min/max that doesn't occur.

Matte

Hm, UINT32_MIN doesn't exist. UINT32_MAX or INT32_MIN – Boorish

@Jens: The two following seem to suggest that such definitions are required 1) opengroup.org/onlinepubs/000095399/basedefs/stdint.h.html 2) linux-documentation.com/en/man/man0p/stdint.h.html – Matte

yes, I know, but my point is that it doesn't require a MIN for an unsigned type, doesn't it, since this is always 0, anyhow. – Boorish

@Jens: Ahhh, the light downs. Thanks! – Matte

Looking for UINT32_MAX only tells you if limits.h has been included, not stdint.h. Sometimes people include the one without the other. – Bergren

Answer 3

If you're on a UNIX system, then you should back-up a step and use a configuration package like autoconf(1) or automake(1). It's designed to handle problems like this.

Precontract

This is an embedded system that doesn't use Unix nor Linux, but ThreadX. Also, it was coded before stdint.h became standard. – Coltish

@Thomas: You probably run the Green Hills compiler on an OS other than ThreadX, such as Linux or Windows, right? Very few embedded compilers are self-hosting. That said, autoconf/automake sound like overkill for this situation, and they solve a different problem: "how do I make my code compile on multiple platforms whether they have stdint.h or not?", not "how do I make my new code that uses stdint.h stop conflicting with this old code that defines some of the same types?" – Orchestral