How to View the Instantiated Code of C Templates?

Seeing the Instantiated Code of C Templates

In C , it can be beneficial to examine the code generated by the compiler for function or class templates. For instance, consider the following template:

<code class="cpp">template <class T> T add(T a, T b) {
    return a + b;
}</code>

When invoked with a specific type, such as add(10, 2), we may want to view the function that the compiler creates for this particular specialization.

Compiler Options to Achieve Visibility

One way to accomplish this is by using the -Xclang -ast-print -fsyntax-only option with Clang. This option instructs the compiler to print the abstract syntax tree (AST) of the instantiated template.

Example Usage

Let's create a test file named test.cpp containing the following code:

<code class="cpp">template <class T> T add(T a, T b) {
    return a + b;
}

void tmp() {
    add<int>(10, 2);
}</code>

To see the instantiated code for the int specialization, run the following command:

$ clang++ -Xclang -ast-print -fsyntax-only test.cpp

Clang Output

For Clang version 5.0 or later, the output will look like this:

template <class T> T add(T a, T b) {
    return a + b;
}
template<> int add<int>(int a, int b) {
    return a + b;
}
void tmp() {
    add<int>(10, 2);
}

This output shows the original template, followed by the specialized add function that the compiler has instantiated.

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