C + + assert () assertion mechanism

C + + assert () assertion mechanism
ASSERT () is a macro that is used frequently when a debugger is run, and it evaluates expressions in parentheses when the program runs, and if the expression is False (0),
The program will report an error and terminate execution. If the expression is not 0, the following statement continues. This macro usually turns out that there is clearly illegal data in the program, and if a termination procedure is used to avoid serious consequences, it is also easy to find errors.

Prototype definition:
#include <assert.h>
void assert (int expression_r_r_r);
The role of assert is to calculate the expression Expression_r_r_r, if its value is false (that is, 0), then it first prints an error message to stderr, and then by calling
Abort to terminate the program run. Take a look at the following program listing BADPTR.C:

#include <stdio.h>
#include <assert.h>
#include <stdlib.h>
int main (void)
{
FILE *FP;

fp = fopen ("Test.txt", "w");//Open a file in a writable manner and create a file with the same name if it does not exist
ASSERT (FP); So there's no mistake here.
Fclose (FP);

fp = fopen ("Noexitfile.txt", "R");//Open a file in a read-only manner and open if it does not exist
ASSERT (FP); So there's a mistake.
Fclose (FP); The program will never be executed here.
return 0;
}
[Email protected] error_process]# gcc badptr.c
[Email protected] error_process]#./a.out
A.out:badptr.c:14:main:assertion ' FP ' failed.
has been abandoned

The disadvantage of using assert is that frequent calls can greatly affect the performance of the program and add additional overhead.
After debugging, you can insert the #define NDEBUG before the statement that contains # include <assert.h>
To disable the Assert call, the sample code is as follows:
#include <stdio.h>
#define Ndebug
#include <assert.h>

Usage Summary and Precautions:
1) Verify the legitimacy of incoming parameters at the beginning of the function
Such as:
int resetbuffersize (int nnewsize)
{
Function: Change buffer size,
Parameter: Nnewsize buffer new length
Return value: Buffer current length
Note: Keep the original information content unchanged nnewsize<=0 means clear buffer
ASSERT (nnewsize >= 0);
ASSERT (Nnewsize <= max_buffer_size);
...
}
2) Each assert examines only one condition, because when multiple conditions are checked, if the assertion fails, it is not possible to visually determine which condition failed
Bad: Assert (noffset>=0 && noffset+nsize<=m_ninfomationsize);
Good: Assert (noffset >= 0);
ASSERT (Noffset+nsize <= m_ninfomationsize);

3) You cannot use a statement that alters the environment, because assert only takes effect in debug, and if you do, you will use the program to run into problems when it is actually running
Error: Assert (i++ < 100)
This is because if there is an error, such as i=100 before execution, then this statement will not be executed, then i++ This command will not be executed.
Correct: Assert (I < 100)
i++;


4) Assert and subsequent statements should be empty lines to create a logical and visual sense of consistency
5) In some places, assert cannot replace conditional filtering


Assert is only valid in debug versions and is ignored if compiled to release version. (in C, assert is a macro instead of a function), using Assert "assert" is easy to output a program error at debug time.
The function of assert () is similar, it is a function specified in the ANSI C standard, and an important difference between it and assert is that it can be used in release version.

C + + assert () assertion mechanism