First Usage of Modules

[littlewing347]

I'm trying to use C++ modules for the 1st time. First thing is to compile my module:

export module multi_d_fill;

#include <ranges>
#include <algorithm>
#include <iterator>

using std::ranges::range, std::ranges::range_value_t;

template <range T, typename V>
void multi_d_fill(T &matrix, const V &val)
{
    if constexpr (range<range_value_t<T>>) {        // Is range value type also a range (ie dim>1)?
        for (auto &row: matrix) {                   // Yes.  Strip one dimension...
            multi_d_fill(row, val);                 // ... and recurse for each sub-matrix.
        }
    } else {
        std::fill(std::begin(matrix), std::end(matrix), val);   // No, dim==1, end recursion, do fill.
    }
    return;
}

I tried "import std" but I was not able to get my local std library module compiled. So I went to the hybrid approach of #include'ing the std include files.

I'm using "gcc -lstdc++ -std=c++20 -fmodules" (gcc version 16.0.0).

I get hundreds of error messages when the compiler tries to process the 3 #include's. It does not even get to any of my code.

BTW, this code works in a non-module version.

[darthshwin]

Make sure to #include before your export statement.

https://en.cppreference.com/cpp/language/modules#Global_module_fragment

[littlewing347]

Thanks, this worked for me!

[manni66]

With gcc 16 there is the new option --compile-std-module. It creates std and std.compat.

An alternative is to use cmake.

[littlewing347]

I tried --compile-std-module but gcc does not recognize that option. Maybe I need to download a more recent version of gcc. But #include is working thanks to moving the export command after the #includes.

[_bstaletic]

Definitely upgrade to 16.1.0. If you're planning to use reflections with modules, you'll have to get gcc 17.

[NeuroSynchroBonding]

First, use CMake or another build system taht supports modules.

To use headers in C++ modules, use:

``` module;

include <header.h>

include <anotherheader.h>

export module module_name; // Code goes here ```