How to make code portable when function names differ between platforms?

I am trying to write code that is portable across Windows and Mac OS X. The problem I have is that I need to read and write large files over 4GB, so I need to use 64 bit versions of fseek() and ftell(). On Windows (using MinGW), I can use fseeko64() and ftello64(). However, these functions do not exist on Mac OS X. It uses ftell(), and I believe supports 64 bit files by default if using 64 bit variables to store file offsets (I am using int64_t).

Another problem is that MinGW doesn't like the %lld printf specifier. It wants %I64d instead. Is there a way I can change these based on a preprocessor statement? Something like this:

Code:

---

#if defined(_WIN32)
#define %lld %I64d
#endif

---

That doesn't work, but you see what I'm getting at.

Quote:

---

Originally Posted by synthetix

I am trying to write code that is portable across Windows and Mac OS X. The problem I have is that I need to read and write large files over 4GB, so I need to use 64 bit versions of fseek() and ftell(). On Windows (using MinGW), I can use fseeko64() and ftello64(). However, these functions do not exist on Mac OS X. It uses ftell(), and I believe supports 64 bit files by default if using 64 bit variables to store file offsets (I am using int64_t).

Another problem is that MinGW doesn't like the %lld printf specifier. It wants %I64d instead. Is there a way I can change these based on a preprocessor statement? Something like this:

Code:

---

#if defined(_WIN32)
#define %lld %I64d
#endif

---

That doesn't work, but you see what I'm getting at.

---

Also don't forget that there are probably endianness issues propping up when working with Mac vs. PC.

The usual trick is something like

Code:

---

#if defined (_WIN32)
#define LONGLONGSPEC %I64d
#else
#define LONGLONGSPEC %lld
#endif

---

I think your endianness issues are probably ok, unless you are on a non-Intel Mac, but it may not hurt to check if you're writing data files that need to cross platforms.

Quote:

---

Originally Posted by tabstop

The usual trick is something like

Code:

---

#if defined (_WIN32)
#define LONGLONGSPEC %I64d
#else
#define LONGLONGSPEC %lld
#endif

---

---

Thanks. That worked but I had to use quotes around the specifiers like this:

Code:

---

#if defined(_WIN32)
#define LONGLONGSPEC "%I64d"
#else
#define LONGLONGSPEC "%lld"
#endif

---

And then I called the printf like this:

Code:

---

printf("Here's a big ol' number: "LONGLONGSPEC"\n", (int64_t)bignum);

---

Quote:

---

I think your endianness issues are probably ok, unless you are on a non-Intel Mac, but it may not hurt to check if you're writing data files that need to cross platforms.

---

The biggest problem I've run into with this is with legacy file formats that want things in big-endian format. QuickTime files are notorious for this, so I have to do endian swaps a lot to make the data valid.

Any idea how to swap out function names based on whether the environment is Windows or Mac? I need ftello64() on Windows, and just ftell() on Mac.

Code:

---

#include <stdio.h>
#include <math.h>

#ifdef MAKEITCOS
#define TRIGFUNC cos
#else
#define TRIGFUNC sin
#endif

int main(void) {
    double result;
    result = TRIGFUNC (0.0);
    printf("%g\n", result);
    return 0;
}

---

You don't have to worry about reaching into quoted string literals this time, like you did last time.

Quote:

---

Originally Posted by tabstop

Code:

---

#include <stdio.h>
#include <math.h>

#ifdef MAKEITCOS
#define TRIGFUNC cos
#else
#define TRIGFUNC sin
#endif

int main(void) {
    double result;
    result = TRIGFUNC (0.0);
    printf("%g\n", result);
    return 0;
}

---

You don't have to worry about reaching into quoted string literals this time, like you did last time.

---

Works great! Thanks!