assert computer语句类似于英语中的make sure语句。

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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

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。

如果Assert的参数为假，Assert将终止程序(通常使用引用Assert语句的消息)。它通常在调试期间使用，以使程序在发生意外情况时更明显地失败。

例如:

assert(length >= 0);  // die if length is negative.

你也可以添加一个信息更丰富的消息显示，如果它失败了，如下所示:

assert(length >= 0 && "Whoops, length can't possibly be negative! (didn't we just check 10 lines ago?) Tell jsmith");

或者像这样:

assert(("Length can't possibly be negative! Tell jsmith", length >= 0));

在进行发布(非调试)构建时，还可以通过定义NDEBUG宏(通常带有编译器开关)来消除求值assert语句的开销。这样做的必然结果是，您的程序永远不应该依赖assert宏运行。

// BAD
assert(x++);

// GOOD
assert(x);    
x++;

// Watch out! Depends on the function:
assert(foo());

// Here's a safer way:
int ret = foo();
assert(ret);

由于程序调用abort()并且不能保证执行任何操作，因此断言应该只用于测试开发人员假设的事情，而不是用于测试用户输入的数字而不是字母(这应该通过其他方式处理)。

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.

assert computer语句类似于英语中的make sure语句。