# std::filesystem::path::append, std::filesystem::path::operator/=

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< cpp‎ | filesystem‎ | path

path& operator/=( const path& p ); | (1) | (since C++17)
template< class Source > path& operator/=( const Source& source ); | (2) | (since C++17)
template< class Source > path& append( const Source& source ); | (3) | (since C++17)
template< class InputIt > path& append( InputIt first, InputIt last ); | (4) | (since C++17)

1) If p.is_absolute() || (p.has_root_name() && p.root_name() != root_name()), then replaces the current path with p as if by operator=(p) and finishes.
* Otherwise, if p.has_root_directory(), then removes any root directory and the entire relative path from the generic format pathname of *this
* Otherwise, if has_filename() || (!has_root_directory() && is_absolute()), then appends `path::preferred_separator` to the generic format of *this
* Either way, then appends the native format pathname of `p`, omitting any root-name from its generic format, to the native format of *this.

    // where "//host" is a root-name
    path("//host")  / "foo" // the result is      "//host/foo" (appends with separator)
    path("//host/") / "foo" // the result is also "//host/foo" (appends without separator)

    // On POSIX,
    path("foo") / ""      // the result is "foo/" (appends)
    path("foo") / "/bar"; // the result is "/bar" (replaces)

    // On Windows,
    path("foo") / "C:/bar";  // the result is "C:/bar" (replaces)
    path("foo") / "C:";      // the result is "C:"     (replaces)
    path("C:") / "";         // the result is "C:"     (appends, without separator)
    path("C:foo") / "/bar";  // yields "C:/bar"        (removes relative path, then appends)
    path("C:foo") / "C:bar"; // yields "C:foo/bar"     (appends, omitting p's root-name)

2,3) Same as (1), but accepts any std::basic_string, std::basic_string_view, null-terminated multicharacter string, or an input iterator pointing to a null-terminated multicharacter sequence. Equivalent to return operator/=(path(source));.
4) Same as (1), but accepts any iterator pair that designates a multicharacter string. Equivalent to return operator/=(path(first, last));

(2) and (3) 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 | - | pathname 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)

### Return value

*this

### Exceptions

May throw std::bad_alloc if memory allocation fails.

### Notes

These functions effectively yield an approximation of the meaning of the argument path `p` in an environment where *this is the starting directory.

### Example

The output is produced on Windows.

Run this code

    #include <iostream>
    #include <filesystem>
    namespace fs = std::filesystem;
    int main() {
        fs::path p1 = "C:";
        p1 /= "Users"; // does not insert a separator
        std::cout << "\"C:\" / \"Users\" == " << p1 << '\n';
        p1 /= "batman"; // inserts fs::path::preferred_separator, '\' on Windows
        std::cout << "\"C:\" / \"Users\" / \"batman\" == " << p1 << '\n';
    }

Possible output:

    "C:" / "Users" == "C:Users"
    "C:" / "Users" / "batman" == "C:Users\\batman"

### 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 3244 | C++17 | constraint that `Source` cannot be `path` was missing | added

### See also

concat operator+= | concatenates two paths without introducing a directory separator (public member function)
operator/ (C++17) | concatenates two paths with a directory separator (function)

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