Upgrade and describe supported toolchains

.travis.yml

@@ -4,6 +4,13 @@ matrix:
       dist: bionic
       language: cpp
       compiler: gcc
+      addons:
+        apt:
+          sources:
+            - ubuntu-toolchain-r-test
+          packages:
+            - g++-8
+      env: CXX=g++-8 CC=gcc-8
     - os: osx
       osx_image: xcode10.2
       language: cpp

README.md

@@ -587,10 +587,13 @@ $ ./main fex
 baz
 ```
 
-## Supported Compilers
-* GCC >= 7.0.0
-* Clang >= 4.0
-* MSVC >= 2017
+## Supported Toolchains
+
+| Compiler             | Standard Library | Test Environment   |
+| :------------------- | :--------------- | :----------------- |
+| GCC >= 8.3.0         | libstdc++        | Ubuntu 18.04       |
+| Clang >= 7.0.0       | libc++           | Xcode 10.2         |
+| MSVC >= 14.16        | Microsoft STL    | Visual Studio 2017 |
 
 ## Contributing
 Contributions are welcome, have a look at the [CONTRIBUTING.md](CONTRIBUTING.md) document for more information.

include/argparse.hpp

@@ -30,6 +30,7 @@ SOFTWARE.
 #pragma once
 #include <algorithm>
 #include <any>
+#include <charconv>
 #include <cstdlib>
 #include <functional>
 #include <iostream>