Executing a Function From the Command or Watch Window

ID: Q67007

The information in this article applies to:

Microsoft CodeView for MS-DOS
Microsoft CodeView for OS/2
Microsoft CodeView for Windows
Microsoft CodeView for Win32s

SUMMARY

According to page 201 of the Microsoft C "Advanced Programming Techniques" manual for versions 6.x, "any C function in your program (whether user-written or from the library) can be called from the Command window or the Watch window."

This statement is not entirely true; you can call only functions compiled with full CodeView symbolic debugging information from the Command and Watch windows. Therefore, you cannot call any functions in the C run-time library because the libraries do not contain symbolic information. The text below provides an example of calling a function in the C run-time library.

In Microsoft C/C++ version 7.0, chapter 11 of the "Environment and Tools" manual documents calling functions from the CodeView command window.

MORE INFORMATION

An attempt to call, from the Command window, a function that does not have any symbolic information fails and CodeView generates an error message. In CodeView versions 4.0x, 4.1, and 4.25, the error is as follows:

CXX0017: Error: symbol not found

-or-

CAN0017: Error: symbol not found

In CodeView versions 3.x, the error is as follows:

CV1017 Error: Syntax error

CodeView versions 2.x display an "unknown symbol" error in the Command window.

An attempt to add to the Watch window a function that does not have any symbolic information fails and CodeView generates an error message. In CodeView versions 4.0x, 4.1, and 4.25, the error is as follows:

CXX0030: Error: expression cannot be evaluated

-or-

CAN0030: Error: expression cannot be evaluated

CodeView versions 3.x ignore the entry and sound the system bell. CodeView versions 2.x generate an "unknown symbol" error.

The Advanced Programming Techniques manual provides an example of calling a function in the C run-time library from the Command window with the following command:

?funcname (varlist)

This command invokes the function and displays its return value in the Command window. To add the function to the Watch window, use the following command:

w?funcname (varlist)

Another method to add a function to the Watch window is as follows: choose Add Watch from the Watch menu. Type the function name, a left parenthesis, the argument list, a right parenthesis, and choose OK. Neither "w" or "?" is required in this situation.

If the function required any input or produces any output, the screen flip/swap option on the Options menu must be selected.

To call a function in the C run-time library, a function in the Windows application programming interface (API), or any other function that does not contain CodeView symbolic information, you must write a shell function that calls the desired function and passes along the value it returns.

For example, to call the sqrt() function in the C run-time library from the CodeView Command or Watch window, create a shell function that looks like the following:

Sample Code


/*
 * Compile options needed: /Zi
 */ 

#include <math.h>

double my_sqrt(double x)
{
   return sqrt(x);
}

Compile this function and link it into your application (be sure to specify the /CO[DEVIEW] LINK option). Your application does not need to call my_sqrt() for the function to be available for direct execution. However, before calling my_sqrt() from the Command or Watch window, you must step into the main() function to initialize the program's stack.

To run the my_sqrt() function from the Command window, type the following:

?my_sqrt(4.0)

CodeView displays the value returned by the function on the next line in the Command window. In this example, CodeView displays 2.0000000000000, the square root of 4.0.

To add the my_sqrt() function to the Watch window, type the following in the Command window:

w?my_sqrt(4.0)

To add the my_sqrt() function to the Watch window using the Add Watch command on the Watch menu, type the following at the Add Watch prompt:

my_sqrt(4.0)

CodeView executes each function in the Watch window each time it updates the Watch window.

Even though these examples use a constant value for the function parameter, you can specify any variable that is currently in scope.

Additional query words: 2.20 3.00 3.50 4.00 4.10 docerr

Keywords : kbcode kbCodeView kbDebug kbVC
Version : :
Platform : MS-DOS OS/2 WINDOWS
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