Files are accessed through the file system using file handles. File handles are returned by DosOpen when the file is opened and are used for all subsequent accesses to the file. Files can be be created, opened, read from, written to, closed, copied, moved, deleted, renamed, and locked. Files can be searched for based on a metacharacter pattern template.
Each open file has a file pointer that indicates the current reading or writing location within the file. The file pointer moves automatically with each read or write operation on the file and can be moved manually by the application.
The standard file handles-standard input, standard output, and standard error-provide redirectable input and output to applications. The standard file handles can be used to read input from the keyboard and write output to the display. Alternatively, they can be redirected to read input from and write output to a file. To an application reading and writing the standard file handles, there is no difference between the two.
Note: In the example code fragments that follow, error checking was left out to conserve space. Applications should always check the return code that the functions return. Control Program functions return an APIRET value. A return code of 0 indicates success. If a non-zero value is returned, an error occurred.