How To Check Characters of File Names and Paths on Windows

C++ Builder has a lot of specific methods in its SysUtils library included in VCL and FMX libraries. Some of these are grouped as Path Manipulation Routines that allow users to edit, extract, get and set drive name, directory name, file name, and file extensions. These methods are combined in Vcl.FileCtrl, System.IOUtils,  System.SysUtils libraries.

These methods are easy to use and easy to get or set file path strings in that operating system. They can be used with other component properties like the FileName property of OpenDialog, SaveDialog components. We can also check drives, files, or directories to see if they exist or not on a given path. You can also check file names and paths to see if it has an extension and has valid, allowable characters in it. For example, on Windows is it not permissible to create a file with a name that contains the “*” (asterisk) character since that is reserved by Windows as a wildcard. Files created with an “*” in their names could result in unexpected and possibly damaging behavior – for example trying to delete a file called “a*.txt” on the command line would actually delete all text files beginning with the letter “a”!

In this post, you’ll learn how to check a file name to see if it has an extension or not, how to check whether a given file name has an extension part, how to check whether a given file name contains only allowed characters, how to check whether a given path string contains only allowed characters, What is HasExtension, HasValidFileNameChars, and HasValidPathChars? By learning how to check file names and paths if they are valid for the Windows operating system. It will help you to easily build C++ applications using the C++ IDE.

What is the C++ HasExtension method ?

The HasExtension Method (System::SysUtils::HasExtension ) is a SysUtils Method that checks whether a given file name has an extension part. We can call HasExtension to check whether a given file name has an extension part. HasExtension returns true if the file name has an extension; false otherwise.

The following table lists the parameters expected by this method:

Name	Meaning
Path	The verified file or directory name

Note: that HasExtension method raises an exception if the given path contains invalid characters.

What is the syntax of HasExtension method?

Here is the Syntax for the HasExtension Method,

What is the C++ HasValidFileNameChars method?

The HasValidFileNameChars Method (System::SysUtils::HasValidFileNameChars) is a SysUtils Method that checks whether a given file name contains only allowed characters. We can call HasValidFileNameChars to check whether a given file name contains only allowed characters. HasValidFileNameChars returns true if the string contains only allowed characters; false otherwise.

The following table lists the parameters expected by this method:

Name	Meaning
Path	The verified file name string.
UseWildcards	Specifies whether the wildcard characters are treated as valid file name characters (e.g. when true we can include asterisk or question marks in the filename although we should not create files containing these characters). With this argument set to True we can know that a filepath such as “C:\myfile\alltextfiles\a*.txt” is valid which we can then use safely as a mask value in the OpenFile dialog functions.

What is the syntax of HasValidFileNameChars method ?

Here is the Syntax for the HasValidFileNameChars

What is the C++ HasValidPathChars method ?

The HasValidPathChars Method (System.SysUtils.ExcludeTrailingBackslash) is a SysUtils Method that checks whether a given path string contains only allowed characters. We can call HasValidPathChars to check whether the given path string contains only allowed characters. HasValidPathChars returns true if the string contains only allowed characters; false otherwise.

The following table lists the parameters expected by this method:

Name	Meaning
Path	The verified path string.
UseWildcards	Specifies whether the wildcard characters are treated as valid path characters (e.g. asterisk or question mark). See above.

What is the syntax of HasValidPathChars method ?

Here is the Syntax for the HasValidPathChars Method:

Here is a full example of how to use the C++ HasExtension, HasValidFileNameChars, HasValidPathChars methods

Here is the full C++ Builder VCL example,

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