std::experimental::filesystem::exists

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< 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)
Concepts (concepts TS)
Extensions for concurrency (concurrency TS)
 
 
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)
represents file type and permissions
(class)
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)