NAME¶

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

Synopsis¶

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

Concatenates the current path and the argument

1-3,6-7) Appends path(p).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.
4-5) Same as return *this += std::basic_string_view(&x, 1);
8) Same as return *this += path(first, last);

(6) and (7) participate in overload resolution only if Source and path are not the
same type, and either:

* Source is a specialization of std::basic_string or std::basic_string_view, or
* std::iterator_traits<std::decay_t<Source>>::value_type is valid and denotes a
possibly const-qualified encoding character type (char,
char8_t,
(since C++20)char16_t, char32_t, or wchar_t).

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
std::basic_string, std::basic_string_view, null-terminated
source - 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¶

// Run this code

#include <iostream>
#include <filesystem>
#include <string>
int main() {
std::filesystem::path p1; // an empty path
p1 += "var"; // does not insert a separator
std::cout << R"("" + "var" --> )" << p1 << '\n';
p1 += "lib"; // does not insert a separator
std::cout << R"("var" + "lib" --> )" << p1 << '\n';
auto str = std::string{"1234567"};
p1.concat(std::begin(str)+3, std::end(str)-1);
std::cout << "p1.concat --> " << p1 << '\n';
}

Output:¶

"" + "var" --> "var"
"var" + "lib" --> "varlib"
p1.concat --> "varlib456"

Defect reports

The following behavior-changing defect reports were applied retroactively to
previously published C++ standards.

DR Applied to Behavior as published Correct behavior
LWG 3055 C++17 the specification of concatenating a single made well-formed
character was ill-formed
LWG 3244 C++17 constraint that Source cannot be path was added
missing

See also¶

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