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

      From cppreference.com
      <cpp‎ |filesystem‎ |path
       
       
      Filesystem library
      Classes
      Functions
      File types
       
      std::filesystem::path
      Member types
      Member 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
       
      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) Appendspath(p).native() to the pathname stored in*this in the native format. This directly manipulates the value ofnative() and may not be portable between operating systems.
      4,5) Same asreturn*this+=std::basic_string_view(&x,1);.
      8) Same asreturn*this+= path(first, last);.

      (6) and(7) participate in overload resolution only ifSource andpath are not the same type, and either:

      Contents

      [edit]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 ofLegacyInputIterators that specify a multicharacter sequence that represents a path name
      Type requirements
      -
      InputIt must meet the requirements ofLegacyInputIterator.
      -
      The value type ofInputIt must be one of the encoded character types (char,wchar_t,char16_t andchar32_t).
      -
      CharT must be one of the encoded character types (char,wchar_t,char16_t andchar32_t).

      [edit]Return value

      *this

      [edit]Exceptions

      May throwstd::bad_alloc if memory allocation fails.

      [edit]Notes

      Unlike withappend() oroperator/=, additional directory separators are never introduced.

      [edit]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 separatorstd::cout<< R"("" + "var" --> )"<< p1<<'\n';    p1+="lib";// does not insert a separatorstd::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"

      [edit]Defect reports

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

      DRApplied toBehavior as publishedCorrect behavior
      LWG 3055C++17the specification of concatenating a single character was ill-formedmade well-formed
      LWG 3244C++17constraint thatSource cannot bepath was missingadded

      [edit]See also

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