1.5 Running a DEC C Program

After you link your program, you can use the DCL command RUN to execute it. The RUN command has the following format:

RUN [/[NO]DEBUG] file-spec [/[NO]DEBUG]

/[NO]DEBUG

An optional qualifier. Specify the /DEBUG qualifier to invoke the debugger if the image was not linked with it. You cannot use /DEBUG on images linked with the /NOTRACEBACK qualifier. If the image was linked with the /DEBUG qualifier and you do not want the debugger to prompt you, use the /NODEBUG qualifier. The default action depends on whether the file was linked with the /DEBUG qualifier.

file-spec

The file you want to run.

The execution of a program begins at the function whose identifier is main, or, if there is no function with this identifier, at the first function seen by the VMS linker.

Note

Unexpected results might occur if you don't have a function called main.

The following example executes the image SAMPLE.EXE without invoking the debugger:

$ RUN SAMPLE/NODEBUG

For more information on debugging programs, see Section C.1.

During execution, an image can generate a fatal error called an exception condition. When an exception condition occurs, the system displays an error message. Run-time errors can also be issued by the operating system or by utilities.

When an error occurs during the execution of a program, the program is terminated and the OpenVMS condition handler displays one or more messages on the currently defined SYS$ERROR device.

A message is followed by a traceback. For each module in the image that has traceback information, the condition handler lists the modules that were active when the error occurred, which shows the sequence in which the modules were called.

For example, if an integer divide-by-zero condition occurs, a run- time message like the following appears:

%SYSTEM-F-INTDIV, arithmetic trap, integer divide by zero
    at PC=00000FC3, PSL=03C00002

This message is followed by a traceback message similar to the following:

%TRACE-F-TRACEBACK, symbolic stack dump follows

module name   routine name   line       rel  PC        abs PC
A             C                 8      00000007      00000FC3
B             main           1408      000002F7      00000B17

The information in the traceback message follows:

module name

The name or names of an image module that was active when the error occurred.

The first module name is that of the module in which the error occurred. Each subsequent line gives the name of the caller of the module named on the previous line. In this example, the modules are A and B; main called C.

routine name

The name of the function in the calling sequence.

line

The compiler-generated line number of the statement in the source program where the error occurred, or at which the call or reference to the next procedure was made. Line numbers in these messages match those in the listing file (not the source file).

rel PC

The value of the PC (program counter). This value represents the location in the program image at which the error occurred or at which a procedure was called. The location is relative to the virtual memory address that the linker assigned to the code program section of the module indicated by module name.

abs PC

The value of the PC in absolute terms; that is, the actual address in virtual memory representing the location at which the error occurred.

Traceback information is available at run time only for modules compiled and linked with the traceback option in effect. The traceback option is in effect by default for both the CC and LINK commands. You may use the CC command qualifier /NODEBUG and the LINK command qualifier /NOTRACEBACK to exclude traceback information. However, traceback information should be excluded only from thoroughly debugged program modules.