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

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C++
 
Filesystem library
Classes
Functions
File types
 
std::filesystem::path
Constants
Member functions
Path decomposition
Non-member functions
(until C++20)(until C++20)(until C++20)(until C++20)(until C++20)(C++20)
Helper Classes
(C++26)
 
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 CharT >
path& operator+=( CharT x );
 (5) (since C++17)
template< class Source >
path& operator+=( const Source& source );
 (6) (since C++17)
template< class Source >
path& concat( const Source& source );
 (7) (since C++17)
template< class InputIt >
path& concat( InputIt first, InputIt last );
 (8) (since C++17)

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:

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

Run this code
#include <filesystem>
#include <iostream>
#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 character was ill-formed made well-formed
LWG 3244 C++17 constraint that Source cannot be path was missing added

See also

 appends elements to the path with a directory separator
(public member function)
(C++17)
 concatenates two paths with a directory separator
(function)
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