DosDebug enables one application to control the execution of another application for debugging purposes.

An application is selected for debugging when it is started. DosExecPgm and DosStartSession both have flags that can be used to specify that the application being started is to be controlled by the starting application.

DosExecPgm starts an application within a new process. DosStartSession starts a new session within which one or more processes can be executing. See DosStartSession and DosExecPgm for details on how to start an application for debugging purposes. For information on processes and sessions, see Program Execution Control in this book.

Once a process has been selected for debugging, DosDebug is used to control its execution and to examine and manipulate its variables.

DosDebug provides a full set of debugging commands, including execution control commands-like single stepping and setting watchpoints-and commands to examine and manipulate the memory and registers of the process being debugged. The debugger process can access specific threads within a process being debugged and specific processes within a session being debugged.

DosDebug also has a rich set of notification messages to keep the debugger application informed of activities occurring during the execution of the application being debugged.

The debugger application can use the session and process control functions described in Program Execution Control to control the child process or session being debugged. For example, the debugger can use DosSelectSession to switch itself, or the session being debugged, to the foreground.