std::filesystem::path::concat, std::filesystem::path::operator+=

path& operator+=( const path& p );	(1)	(since C++17)
path& operator+=( const string_type& str ); path& operator+=( std::basic_string_view<value_type> str );	(2)	(since C++17)
path& operator+=( const value_type* ptr );	(3)	(since C++17)
path& operator+=( value_type x );	(4)	(since C++17)
template< class Source > path& operator+=( const Source& source );	(5)	(since C++17)
template< class CharT > path& operator+=( CharT x );	(6)	(since C++17)
template< class Source > path& concat( const Source& source );	(7)	(since C++17)
template< class InputIt > path& concat( InputIterator first, InputIterator last );	(8)	(since C++17)

Concatenates the current path and the argument.

1-7) Appends path(other).native() to the pathname stored in *this in the native format. This directly manipulates the value of native() and may not be portable between operating systems.

8) Same as return *this += path(first, last)

Parameters

p	-	path to append
str	-	string or string view to append
ptr	-	pointer to the beginning of a null-terminated string to append
x	-	single character to append
source	-	`std::basic_string`, `std::basic_string_view`, null-terminated multicharacter string, or an input iterator pointing to a null-terminated multicharacter sequence, which represents a path name (either in portable or in native format)
first, last	-	pair of LegacyInputIterators that specify a multicharacter sequence that represents a path name
Type requirements
-`InputIt` must meet the requirements of LegacyInputIterator.
-The value type of `InputIt` must be one of the encoded character types (`char`, `wchar_t`, `char16_t` and `char32_t`)
-`CharT` must be one of the encoded character types (`char`, `wchar_t`, `char16_t` and `char32_t`)

Return value

*this.

Exceptions

May throw std::bad_alloc if memory allocation fails.

Notes

Unlike with append() or operator/=, additional directory separators are never introduced.

Example

#include <iostream>
#include <filesystem>
namespace fs = std::filesystem;
int main() {
    fs::path p1; // empty path
    p1 += "var"; // does not insert a separator
    std::cout << "\"\" + \"var\" == " << p1 << '\n';
    p1 += "lib"; // does not insert a separator
    std::cout << "\"\" + \"var\" + \"lib\" == " << p1 << '\n';
}

Output:

"" + "var" == "var"
"" + "var" + "lib" == "varlib"

appendoperator/=	appends elements to the path with a directory separator (public member function)
operator/	concatenates two paths with a directory separator (function)