File and Directory Management

The standard MS-DOS file and directory management functions do not accept long file names. You must, therefore, use the long file name functions to create and manage files and directories having long names. The long file name functions are similar to existing MS-DOS system functions. You copy function parameters to registers and issue an Interrupt 21h instruction to carry out the call. The function sets or clears the carry flag to indicate whether the operation was successful and may also return information in registers.

If a long file name function has a corresponding MS-DOS function, the number that identifies the long file name function is four digits long, beginning with the number 71 and ending in the same number as the corresponding MS-DOS function. For example, the long file name function Make Directory (Interrupt 21h Function 7139h) corresponds to MS-DOS Create Directory (Interrupt 21h Function 39h).

You can create or open a file having a long file name by using Create or Open File (Interrupt 21h Function 716Ch). This function takes the name and attributes of the file to create or open and returns a handle that you use to identify the file in subsequent calls to standard MS-DOS functions, such as Read File or Device (Interrupt 21h Function 3Fh) and Write File or Device (Interrupt 21h Function 40h).

You can set or retrieve the time and attributes for a file having a long file name by using Get or Set File Time (Interrupt 21h Function 57h) and Get or Set File Attributes (Interrupt 21h Function 7143h). You can move a file having a long file name by using Rename File (Interrupt 21h Function 7156h) or delete the file by using Delete File (Interrupt 21h Function 7141h).

You can create a directory having a long file name by using Make Directory (Interrupt 21h Function 7139h) or remove the directory by using Remove Directory (Interrupt 21h Function 713Ah).

You can set and retrieve the current directory by using Change Directory (Interrupt 21h Function 713Bh) and Get Current Directory (Interrupt 21h Function 7147h).