How do you debug heavily templated code in c++? [duplicate]

Answer 1

Templight : A C++ Template Metaprogram Debugger and Profiler

Answer 2

You can try using a newer compiler. If you're using Visual C++ 6.0, switch to 9.0 and you'll see a huge jump in the helpfulness of the compiler errors.

Otherwise, my techniques are usually been to test out as small a section of code as possible until I get the errors isolated. This is probably the template system's greatest failing - there is no sensible way of debugging them.

In your own code, make liberal use of compile-time asserts to make usage problems a little easier to diagnose.

Answer 3

As the answers already illustrate, there are basically 2 types of difficulties in template code: 1. getting it to compile, and find the cause for compiler errors 2. getting it do do the right thing during runtime

I usually try to separate compile time type magic from run time logic, this helps with finding the cause of the problem (Type 1 or 2). A way to achieve this is to use one template type for type magic, and as little as possible run-time functionality, and one plain type for run-time logic, that uses the template type.

If you then follow the advices from the other replies, especially the one about compile_time asserts, it will be easier to find the source of trouble.

Answer 4

For the STL at least there are tools available that will output more human-friendly error messages. See http://www.bdsoft.com/tools/stlfilt.html

For non-STL templates you'll just have to learn what the errors mean. After you've seen them a dozen times it becomes easier to guess what the problem is. If you post them here maybe somebody can help you figure it out.

Answer 5

When making something complicated in meta-programming language, i use the BOOST_MPL_ASSERT macro multiple times, checking the results of every step of the meta-execution. The Boost.MPL library is very useful for that matter. I suggest you use as much code from there as possible, because it's likely it won't contain errors.

When i am not so sure the right specialization for a class is being used, i tend to isolate the right specialization in a namespace. Once you are sure that specialization is valid, you have to make sure that it is chosen. If it's not, you have to find out which one is chosen in its place. Then i'd recommend using Boost.EnableIf to exclude this wrongly-accepted specialization from the selection process.

Last but not least, STLfilt is extremely useful, and you can modify it yourself so that it suits your needs as well as possible.

But the most important thing is to try not to use meta-programming everywhere. It is complicated, so use it only when you really need it.

Answer 6

Metashell is a great tool for template debugging. With online mode!