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 LegacyInputIterator s 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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