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

// 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) 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

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

#include <filesystem>
#include <iostream>
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';
}

"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.

See also