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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) Concatenates *this and p in such a way that native() of the result is exactly original native() concatenated with p.native()

2) Same as (1), except the resulting native() is a concatenation of the original {native() and the string (or string view) str

3) Same as (1), except the resulting native() is a concatenation of the original native() and the null-terminated string whose first character is pointed to by ptr

4) Same as (1), except the resulting native() is a concatenation of the original native() and the single character x

5) Same as (1), except the resulting native() is a concatenation of the original native() and the sequence (which may be in portable or native format) represented by source, which may be std::basic_string, std::basic_string_view, null-terminated multicharacter string, or an input iterator pointing to a null-terminated multicharacter sequence.

6) Same as (4), except that character conversion may be performed

7) Same as (5)

8) Same as (5), except that the sequence is represented by any iterator pair that designates a multicharacter string.

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 `InputIterator`s that specify a multicharacter sequence that represents a path name
Type requirements
- `InputIt` must meet the requirements of `InputIterator`.
-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 filesystem_error on underlying OS API errors or 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"