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assert() c++示例程序

Many compilers offer an assert() macro. The assert() macro returns TRUE if its parameter evaluates TRUE and takes some kind of action if it evaluates FALSE. Many compilers will abort the program on an assert() that fails; others will throw an exception One powerful feature of the assert() macro is that the preprocessor collapses it into no code at all if DEBUG is not defined. It is a great help during development, and when the final product ships there is no performance penalty nor increase in the size of the executable version of the program.

Eg

#include <stdio.h>
#include <assert.h>

void analyze (char *, int);

int main(void)
{
   char *string = "ABC";
   int length = 3;

   analyze(string, length);
   printf("The string %s is not null or empty, "
          "and has length %d \n", string, length);
}

void analyze(char *string, int length)
{
   assert(string != NULL);     /* cannot be NULL */
   assert(*string != '\0');    /* cannot be empty */
   assert(length > 0);         /* must be positive */
}

/****************  Output should be similar to  ******************
The string ABC is not null or empty, and has length 3

c++ 11 N3337标准草案

http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2012/n3337.pdf

19.3断言

头文件<cassert>，如表42所示，提供了一个宏，用于记录c++程序断言 以及禁用断言检查的机制。 2内容与标准C库头文件<assert.h>相同。

c99n1256标准草案

http://www.open-std.org/JTC1/SC22/WG14/www/docs/n1256.pdf

7.2诊断<assert.h> .h

1 The header <assert.h> defines the assert macro and refers to another macro, NDEBUG which is not defined by <assert.h>. If NDEBUG is defined as a macro name at the point in the source file where <assert.h> is included, the assert macro is defined simply as #define assert(ignore) ((void)0) The assert macro is redefined according to the current state of NDEBUG each time that <assert.h> is included. 2. The assert macro shall be implemented as a macro, not as an actual function. If the macro definition is suppressed in order to access an actual function, the behavior is undefined.

7.2.1程序诊断

7.2.1.1 assert宏

Synopsis 1. #include <assert.h> void assert(scalar expression); Description 2 The assert macro puts diagnostic tests into programs; it expands to a void expression. When it is executed, if expression (which shall have a scalar type) is false (that is, compares equal to 0), the assert macro writes information about the particular call that failed (including the text of the argument, the name of the source file, the source line number, and the name of the enclosing function — the latter are respectively the values of the preprocessing macros __FILE__ and __LINE__ and of the identifier __func__) on the standard error stream in an implementation-defined format. 165) It then calls the abort function. Returns 3 The assert macro returns no value.

看一看

assert() c++示例程序

Many compilers offer an assert() macro. The assert() macro returns TRUE if its parameter evaluates TRUE and takes some kind of action if it evaluates FALSE. Many compilers will abort the program on an assert() that fails; others will throw an exception One powerful feature of the assert() macro is that the preprocessor collapses it into no code at all if DEBUG is not defined. It is a great help during development, and when the final product ships there is no performance penalty nor increase in the size of the executable version of the program.

Eg

#include <stdio.h>
#include <assert.h>

void analyze (char *, int);

int main(void)
{
   char *string = "ABC";
   int length = 3;

   analyze(string, length);
   printf("The string %s is not null or empty, "
          "and has length %d \n", string, length);
}

void analyze(char *string, int length)
{
   assert(string != NULL);     /* cannot be NULL */
   assert(*string != '\0');    /* cannot be empty */
   assert(length > 0);         /* must be positive */
}

/****************  Output should be similar to  ******************
The string ABC is not null or empty, and has length 3

此外，您还可以使用它来检查动态分配是否成功。

代码示例:

int ** p;
p = new int * [5];      // Dynamic array (size 5) of pointers to int
for (int i = 0; i < 5; ++i) {
    p[i] = new int[3]; // Each i(ptr) is now pointing to a dynamic
                       // array (size 3) of actual int values
}

assert (p);            // Check the dynamic allocation.

类似于:

if (p == NULL) {
    cout << "dynamic allocation failed" << endl;
    exit(1);
}

使用assert()函数而不是普通的if else和printf有三个主要原因

assert() function is mainly used in the debugging phase, it is tedious to write if else with a printf statement everytime you want to test a condition which might not even make its way in the final code. In large software deployments , assert comes very handy where you can make the compiler ignore the assert statements using the NDEBUG macro defined before linking the header file for assert() function. assert() comes handy when you are designing a function or some code and want to get an idea as to what limits the code will and not work and finally include an if else for evaluating it basically playing with assumptions.

它是一个函数，如果它计算的值为false，则将停止程序执行。通常它被宏包围，这样在使用发布设置编译时就不会编译到结果二进制文件中。

它被设计用来测试你所做的假设。例如:

void strcpy(char* dest, char* src){
    //pointers shouldn't be null
    assert(dest!=null);
    assert(src!=null);

    //copy string
    while(*dest++ = *src++);
}

理想的情况是，您可以在程序中犯错误，例如调用带有无效参数的函数，并且在它发生段错误(或未能按预期工作)之前命中断言。