View function template instantiations

Question

I have a simple function template:

#include <iostream>
using namespace std;

template <class T>
T GetMax (T a, T b) {
  T result;
  result = (a > b) ? a : b;
  return (result);
}

int main () {
  cout << GetMax<int>(5, 6) << endl;
  cout << GetMax<long>(10, 5) << endl;
  return 0;
}

The above example will generate 2 function template instantiations, one for int and another for long. Is there any g++ option to view the function template instantiations?

Answer 1

If you have the linker generate a map file, you can see the names of all generated symbols. Some parsing with grep/perl may get you what you want. The names will be mangled.

This command line worked for me:

g++ -o test -Wl,-map,test.map test.cpp

test.map will be generated.

This might be further down the pipeline than you're looking for though.

Answer 2

You can use the nm program (part of binutils) to see the list of symbols used by your program. For example:

$ g++ test.cc -o test
$ nm test | grep GetMax
00002ef0 T __Z6GetMaxIiET_S0_S0_
00002f5c T __Z6GetMaxIiET_S0_S0_.eh
00002f17 T __Z6GetMaxIlET_S0_S0_
00002f80 T __Z6GetMaxIlET_S0_S0_.eh

I don't know why each one has two copies, one with a .eh suffix, but otherwise you can tell that this particular function was instantiated twice. If you version of nm supports the -C/--demangle flag, you can use that to get readable names:

$ nm --demangle test | grep GetMax
00002ef0 T int GetMax<int>(int, int)
00002f5c T _Z6GetMaxIiET_S0_S0_.eh
00002f17 T long GetMax<long>(long, long)
00002f80 T _Z6GetMaxIlET_S0_S0_.eh

If that option isn't supported, you can use c++filt to demangle them:

$ nm test | grep GetMax | c++filt
00002ef0 T int GetMax<int>(int, int)
00002f5c T __Z6GetMaxIiET_S0_S0_.eh
00002f17 T long GetMax<long>(long, long)
00002f80 T __Z6GetMaxIlET_S0_S0_.eh

So, you can see that GetMax was instantiated with int and long respectively.