Extract base path from a pathname in C

Question

Question

How do you extract the base path from pathname in C?

Are there any functions built into the C language or the C-Runtime L

Answer 1

On Windows there is _splitpath.

Example

#include <Windows.h>
#include <tchar.h>

// Use your own error codes here
#define SUCCESS                     0L
#define FAILURE_NULL_ARGUMENT       1L
#define FAILURE_API_CALL            2L
#define FAILURE_INSUFFICIENT_BUFFER 3L

DWORD GetBasePathFromPathName( LPCTSTR szPathName,
                               LPTSTR  szBasePath,
                               DWORD   dwBasePathSize )
{
  TCHAR   szDrive[_MAX_DRIVE] = { 0 };
  TCHAR   szDir[_MAX_DIR]     = { 0 };
  TCHAR   szFname[_MAX_FNAME] = { 0 };
  TCHAR   szExt[_MAX_EXT]     = { 0 };
  size_t  PathLength;
  DWORD   dwReturnCode;

  // Parameter validation
  if( szPathName == NULL || szBasePath == NULL )
  {
    return FAILURE_NULL_ARGUMENT;
  }

  // Split the path into it's components
  dwReturnCode = _tsplitpath_s( szPathName, szDrive, _MAX_DRIVE, szDir, _MAX_DIR, szFname, _MAX_FNAME, szExt, _MAX_EXT );
  if( dwReturnCode != 0 )
  {
    _ftprintf( stderr, TEXT("Error splitting path. _tsplitpath_s returned %d.\n"), dwReturnCode );
    return FAILURE_API_CALL;
  }

  // Check that the provided buffer is large enough to store the results and a terminal null character
  PathLength = _tcslen( szDrive ) + _tcslen( szDir );
  if( ( PathLength + sizeof( TCHAR ) ) > dwBasePathSize )
  {
    _ftprintf( stderr, TEXT("Insufficient buffer. Required %d. Provided: %d\n"), PathLength, dwBasePathSize );
    return FAILURE_INSUFFICIENT_BUFFER;
  }

  // Copy the szDrive and szDir into the provide buffer to form the basepath
  if( ( dwReturnCode = _tcscpy_s( szBasePath, dwBasePathSize, szDrive ) ) != 0 )
  {
    _ftprintf( stderr, TEXT("Error copying string. _tcscpy_s returned %d\n"), dwReturnCode );
    return FAILURE_API_CALL;
  }
  if( ( dwReturnCode = _tcscat_s( szBasePath, dwBasePathSize, szDir ) ) != 0 )
  {
    _ftprintf( stderr, TEXT("Error copying string. _tcscat_s returned %d\n"), dwReturnCode );
    return FAILURE_API_CALL;
  }
  return SUCCESS;
}

Answer 2

I think the best solution on Windows is to use _splitpath as was suggested, to use something like basename on Linux (more on that here).

That said, since someone has already suggested implementing my own (and since I had already done it while I was waiting for an answer), here is what I came up with. It is not cross-platform and it does not check for /valid/ paths or expand short or relative path names.

// Retrieves the pathpath from a pathname.
//
// Returns: SUCCESS if the basepath is present and successfully copied to the p_base_path buffer
//          FAILURE_NULL_ARGUMENT if any arguments are NULL
//          FAILURE_INVALID_ARGUMENTS if either buffer size is less than 1
//          FAILURE_BUFFER_TOO_SMALL if the p_basepath buffer is too small
//          FAILURE_INVALID_PATH if the p_pathname doesn't have a path (e.g. C:, calc.exe, ?qwa)
//          FAILURE_API_CALL if there is an error from the underlying API calls
int get_base_path_from_pathname( const char*  const p_pathname,
                                 size_t             pathname_size,
                                 char* const        p_basepath,
                                 size_t             basepath_size );

int get_base_path_from_pathname( const char*  const p_pathname,
                                 size_t             pathname_size,
                                 char* const        p_basepath,
                                 size_t             basepath_size )
{
  char*  p_end_of_path;
  size_t path_length;
  int    return_code;

  // Parameter Validation
  if( p_pathname == NULL || p_basepath == NULL ) { return FAILURE_NULL_ARGUMENT; }
  if( pathname_size < 1 || basepath_size < 1 ) { return FAILURE_INVALID_ARGUMENTS; }

  // Returns a pointer to the last occurrence of \ in p_pathname or NULL if it is not found
  p_end_of_path = strrchr( p_pathname, '\\' );
  if( p_end_of_path == NULL )
  {
    // There is no path part
    return FAILURE_INVALID_PATH;
  } 
  else 
  {
    path_length = (size_t)( p_end_of_path - p_pathname + 1 );

    // Do some sanity checks on the length
    if( path_length < 1 ) { return FAILURE_INVALID_PATH; }
    if( ( path_length + 1 ) > basepath_size ) { return FAILURE_BUFFER_TOO_SMALL; }

    // Copy the base path into the out variable
    if( strncpy( p_basepath, p_pathname, path_length ) != 0 ) { return FAILURE_API_CALL; }
    p_basepath[path_length] = '\0';
  }

  return SUCCESS;
}