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This article introduces the relevant knowledge of "what is the use of the C language assertion function assert ()". In the operation of actual cases, many people will encounter such a dilemma, so let the editor lead you to learn how to deal with these situations. I hope you can read it carefully and be able to achieve something!

   provides a small library of auxiliary debug programs in C language library functions, which is composed of assert () macros and receives an integer expression as a parameter. If the value of the expression is false (non-zero), the assert () macro writes an error message to the standard error stream (stderr) and calls the abort () function to terminate the program.

   Let's take a look at the use of assert () with a simple example.

Int main () {int n = 1; assert (n > = 0); printf ("% d\ r\ n", n); system ("pause"); return 0;}

   in assert () determines that the condition of the expression is n > 0, then when the value of the integer variable n is less than 0, the expression is false and the assertion function will work. Let's try the normal situation first. Set the value of n to 1, and the output is as follows:

   then changes the value of n to-1 to continue the test.

   the program terminated abnormally at this time. Let's take a detailed analysis of the execution of this function.

   can see the prototype of assert () in the assert. H header file. There are two prototypes, one is that the first assert () is called when _ UNICODE or UNICODE is defined, and when there is no definition, the second assert () is called. Since there is no _ UNICODE or UNICODE defined in the header file, the second assert is called here. Let's start by analyzing this macro definition statement.

# define assert (_ Expression) (void) ((!! (_ Expression)) | | (_ assert (# _ Expression,__FILE__,__LINE__), 0) void _ _ cdecl _ assert (const char * _ Message, const char * _ File, unsigned _ Line)

   first passes a parameter _ Expression into the assert, followed by a statement in which two parts are connected by the OR operator. For the or operator | |, the second condition is not executed when the first condition is true, and the second statement is executed only when the first condition is not true.

((!) (_ Expression)) | | (_ assert (# _ Expression,__FILE__,__LINE__), 0))

   first looks at the first judgment condition (!! (_ Expression)). It takes two negatives to the passed parameter, which is equivalent to the variable itself. When _ Expression is true, the second condition will not be executed, and only if _ Expression is false will the second condition be executed. In the program, the second condition is not executed when n > 0 is established, and the second statement is executed when n > 0 is not true, so in the above test, the program terminates abnormally when n =-1.

   next looks at the second condition (_ assert (# _ Expression,FILE,LINE), 0), which is a function whose prototype is:

Void _ _ cdecl _ assert (const char * _ Message, const char * _ File, unsigned _ Line)

The    function has three parameters, and it can be inferred from the names of these three parameters that the first parameter is used to store the content of the information, the second parameter is used to represent the details of the current file, and the third parameter indicates which line in the code is wrong.

The three parameters of    are consistent with the contents printed by the console. Program is followed by the currently running executable file path, File is followed by the error file path, Line is followed by the specific location of the error, indicating that there is an error in the 16th line of the program in the test6.c file, and the last line indicates that the error expression is n > = 0, indicating that the condition that the variable n is greater than or equal to 0 is not valid. That is, the value of the current variable n is less than 0, so a program exception is thrown.

   can see from the above analysis that assert () is very helpful for debugging programs. Errors like this hidden in the code cannot be detected by the compiler when the program is compiled, and will only be found when the program is executed. So using assert () to detect the expression can quickly locate the program's bug.

   join does not want to use assert () to detect, do not need to modify the code, just need to define NDEBUG in assert.h.

  adds a macro definition to assert.h and continues to run the program.

   at this time the value of n is-1, but the program prints out-1 normally and does not report an error. Indicates that assert () no longer detects errors. This can also be seen in the header file.

When    defines NDEBUG, the specific function executed by * * assert (_ Expression) * * becomes ((void) 0), that is, doing nothing. So when NDEBUG is defined in the header file, the detection function of assert () automatically fails. In this way, when debugging the program, only one statement is needed to turn the debugging information output on or off.

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