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std::experimental::filesystem::exists

From cppreference.com
< cpp‎ | experimental‎ | fs
 
 
Technical specifications
Filesystem library (filesystem TS)
Library fundamentals (library fundamentals TS)
Library fundamentals 2 (library fundamentals 2 TS)
Extensions for parallelism (parallelism TS)
Extensions for concurrency (concurrency TS)
Concepts (concepts TS)
Ranges (ranges TS)
Special mathematical functions (special math TR)
 
 
Defined in header <experimental/filesystem>
bool exists( file_status s )
(1) (filesystem TS)
bool exists( const path& p );
bool exists( const path& p, error_code& ec )
(2) (filesystem TS)

Checks if the given file status or path corresponds to an existing file or directory.

1) Equivalent to status_known(s) && s.type() != file_type::not_found.
2) Equivalent to exists(status(p)) or exists(status(p, ec)) (symlinks are followed). The non-throwing overload returns false if an error occurs.

Contents

[edit] Parameters

s - file status to check
p - path to examine
ec - out-parameter for error reporting in the non-throwing overload

[edit] Return value

true if the given path or file status corresponds to an existing file or directory, false otherwise.

[edit] Exceptions

1)
noexcept specification:  
noexcept
  
2) The overload that does not take a error_code& parameter throws filesystem_error on underlying OS API errors, constructed with p as the first argument and the OS error code as the error code argument. std::bad_alloc may be thrown if memory allocation fails. The overload taking a error_code& parameter sets it to the OS API error code if an OS API call fails, and executes ec.clear() if no errors occur. This overload has
noexcept specification:  
noexcept
  

[edit] Notes

The information provided by this function is usually also provided as a byproduct of directory iteration. During directory iteration, calling exists(*iterator) is less efficient than exists(iterator->status())

[edit] Example

#include <iostream>
#include <fstream>
#include <cstdint>
#include <experimental/filesystem>
namespace fs = std::experimental::filesystem;
 
void demo_exists(const fs::path& p, fs::file_status s = fs::file_status{})
{
    std::cout << p;
    if(fs::status_known(s) ? fs::exists(s) : fs::exists(p))
        std::cout << " exists\n";
    else
        std::cout << " does not exist\n";
}
int main()
{
    fs::create_directory("sandbox");
    std::ofstream("sandbox/file"); // create regular file
    fs::create_symlink("non-existing", "sandbox/symlink");
 
    demo_exists("sandbox");
    for(auto it = fs::directory_iterator("sandbox"); it != fs::directory_iterator(); ++it)
        demo_exists(*it, it->status()); // use cached status from directory entry
    fs::remove_all("sandbox");
}

Output:

"sandbox" exists
"sandbox/file" exists
"sandbox/symlink" does not exist

[edit] See also

determines file attributes
determines file attributes, checking the symlink target
(function) [edit]
represents file type and permissions
(class) [edit]
cached status of the file designated by this directory entry
cached symlink_status of the file designated by this directory entry
(public member function of std::experimental::filesystem::directory_entry) [edit]