Determining OpenSSL version with ifdef

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I've written code that under certain circumstances might load X509_STORE into SSL_CTX, and since I don't know if it happens I free the store at the end of the program.

I call X509_STORE_up_ref after loading the store into the context to avoid a reference count error, since SSL_CTX_free also frees the store in case it was loaded into the given context.

However, I noticed that X509_STORE_up_ref is a newer command and my program fails to compile on older systems. I'd like in that case to wrap the call to that function with an #ifdef for OpenSSL's version.

  1. What is the right way to check OpenSSL's version with an #ifdef?
  2. Am I right to even be in the position I'm in, or am I using the store the wrong way?
openssl c
2 Answers

You can check the OpenSSL version number by looking at the OPENSSL_VERSION_NUMBER macro. The opensslv.h file contains the following comments regarding its value:

/*-
 * Numeric release version identifier:
 * MNNFFPPS: major minor fix patch status
 * The status nibble has one of the values 0 for development, 1 to e for betas
 * 1 to 14, and f for release.  The patch level is exactly that.
 * For example:
 * 0.9.3-dev      0x00903000
 * 0.9.3-beta1    0x00903001
 * 0.9.3-beta2-dev 0x00903002
 * 0.9.3-beta2    0x00903002 (same as ...beta2-dev)
 * 0.9.3          0x0090300f
 * 0.9.3a         0x0090301f
 * 0.9.4          0x0090400f
 * 1.2.3z         0x102031af

So if for example you had a certain feature that required OpenSSL 1.1.0 or higher you would do this:

#if OPENSSL_VERSION_NUMBER >= 0x10100000L
// code for version 1.1.0 or greater
#else
// core for 1.0.x or lower
#endif
user_16871190

An #ifdef will only tell you at compile-time whether you are compiling your code with a version of the OpenSSL SDK that supports the function you want to call. But it will not tell you at runtime whether the OpenSSL binaries actually contain that function. So, you would have to ensure that you are actually using the correct binaries that match the SDK you compiled with. Or else load the function dynamically at runtime, such as with GetProcAddress() on Windows, dlsym() on Linux, etc.

user_658630
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