Introduction to the implementation of trace and assert macros

Below is a relatively simple Win32 Implementation of trace and assert:

# Define assert (expr )/

Do {/

If (! (Expr )&&/

(1 = _ crtdbgreport (_ crt_assert, _ file __, _ line __, null, # expr )))/

_ ASM {INT 3 };/

} While (0)

 

# Define trace (expr )/

_ Crtdbgreport (_ crt_warn, _ file __, _ line __, null, expr)

 

All of them call the _ crtdbgreport function. Its prototype is as follows:

_ Cribd int _ cdecl _ crtdbgreport (

Int nrpttype,

Const char * szfile,

Int nline,

Const char * szmodule,

Const char * szformat,

...

);

 

The first parameter of _ crtdbgreport indicates the type of the report message. There are three types:

# DEFINE _ crt_warn 0

# DEFINE _ crt_error 1

# DEFINE _ crt_assert 2

The implementation of the _ crtdbgreport function is to splice the report message first, and then send the message to the appropriate place based on the message type, as shown below:

First, judge the value of _ crtdbgmode [nrpttype ].

_ Crtdbgmode [0] = 2;

_ Crtdbgmode [1] = 4;

_ Crtdbgmode [2] = 4;

The system defines the following macro to describe where these report messages are sent,

# DEFINE _ crtdbg_mode_file 0x1

# DEFINE _ crtdbg_mode_debug 0x2

# DEFINE _ crtdbg_mode_wndw 0x4

With the help of the source code and msdn, I finally figured out the location of the message:

If _ crtdbgmode [nrpttype] is _ crtdbg_mode_debug, call outputdebugstring to send the report message to the debugger.

If _ crtdbgmode [nrpttype] is _ crtdbg_mode_wndw, a dialog box with three buttons is displayed: Terminate, retry, and ignore.

Let's look back at the assert macro. Obviously, if the expr is non-zero, the assert is successful, and the while loop is exited directly without executing _ crtdbgreport. If the expr is 0, the _ crtdbgreport is executed, if you choose to terminate, the application is terminated immediately. If you choose to retry, _ crtdbgreport returns 1. The program runs the following Assembly Statement, which interrupts the program, it is the same as when you set a breakpoint. If you select ignore, the program continues to run. By the way, # expr indicates converting expr to a string. For example, if assert (0 = I), # expr is "0 = I".

If _ crtdbgmode [nrpttype] is _ crtdbg_mode_file, the report information is written into the file indicated by _ crtdbgfile [nrpttype.

The non-Win32 Implementation of the trace macro is very simple, that is, the printf is called to directly output the report message.