断言失败的vc++文档

In this article, we’ll take a look at using the concept of assertions, using the assert in C/C++.

在本文中，我们将研究使用断言的概念，以及在C / C ++中使用断言。

This is not very hard to understand, so let’s get started!

这不是很难理解的，所以让我们开始吧！

We’ll first look at what we mean by an assertion, and then look at how we can use it in our C programs to debug effectively!

我们将首先了解断言的含义，然后了解如何在C程序中使用它来有效调试！

什么是断言？ (What is an assertion?)

An assertion is a specification that verifies that a program satisfies certain conditions at particular points, during its execution (run-time condition checks).

断言是一种规范，用于在程序执行期间（运行时条件检查）验证程序在特定点上满足某些条件。

For computer programs, there are primarily three types of assertions checks:

对于计算机程序，主要有三种断言检查类型：

• Precondition Assertion -> Condition satisfied before main body execution前提条件断言 ->执行主体之前满足条件
• Post-condition Assertion -> Condition satisfied after main body execution后置条件声明 ->执行主体后满足条件
• Invariant Assertion -> Condition satisfied after every repetitive region of a function (like a loop)不变断言 ->在函数的每个重复区域之后都满足条件（例如循环）

Now that we know what an assertion is, let’s look at doing this in a C program.

现在我们知道了什么是断言，让我们来看一下在C程序中执行此操作的过程。

在C程序中使用断言 (Using assertions in C programs)

In C, we use the assert macro to define an assertion statement. This is there in the <assert.h> header file.

在C语言中，我们使用assert宏定义断言语句。 在<assert.h>头文件中。

To define an assertion, we can write something like this:

要定义一个断言，我们可以这样写：

#include <assert.h>assert (condition);

Here, condition must be boolean. For example, the below is an example of an assertion:

在此， condition必须为布尔值。 例如，以下是断言的示例：

int i=0;
assert (i >= 0);

The above assertion holds true, since 0>=0. Therefore, during execution, our program continues normally.

上面的断言成立，因为0>=0 。 因此，在执行过程中，我们的程序可以正常继续。

If the assert condition holds false, it will produce an error, and our program will stop executing, with suitable error messages.

如果断言条件为假，它将产生一个错误，并且我们的程序将停止执行，并显示适当的错误消息。

int i = 0;
// This is false
assert (i > 0);

Now that we’ve covered the basics, let’s look at using assertions in a for loop.

现在我们已经介绍了基础知识，让我们看一下在for循环中使用断言。

This not only ensures that we want the program to do what we want, but also structures code logically, so that it is easy to read.

这不仅可以确保我们希望程序执行所需的操作，而且还可以逻辑地构造代码，以便于阅读。

一个示例–在循环中使用assert (An example – Using assert in a loop)

Consider the below code, that simply adds integers within a given range. We want to ensure that our final result is always positive, and does not overflow.

考虑下面的代码，该代码仅将给定范围内的整数相加。 我们要确保我们的最终结果始终是积极的，并且不会溢出。

#include <stdio.h>
#include <limits.h>
#include <assert.h>int loop_function(int a, int b) {// Precondition assertion (a <= b)assert (a <= b);int result = 0;for (int i=a; i<=b; i++) {// Invariant assertion// The cummulative result must always be positive// Sometimes, the result may overflow and give a negative// integer. In that case, this assertion will failassert (result >= 0);result += i;}// Postcondition assertion// Again, the net result must be positive// So if result = 0, this condition will failassert (result > 0);return result;
}int main() {int a = 3;int b = 10;printf("loop_function on %d and %d gives %d\n", a, b, loop_function(a, b));int c = INT_MAX - 3;int d = INT_MAX;// Here, in case of c and d, the result will overflow. The invariant assertion will be false!printf("loop_function on %d and %d gives %d\n", c, d, loop_function(c, d));return 0;
}

Output

输出量

loop_function on 3 and 10 gives 52
assert_loop: assert_loop.c:14: loop_function: Assertion `result >= 0' failed.
[1]    337 abort (core dumped)  ./assert_loop

If the value of our result is too high (beyond the integer size), then the result will overflow and become negative!

如果结果的值太高（超出整数大小），则结果将溢出并变为负数！

Our second set of input does this, and hence the loop invariant assertion will fail!

我们的第二组输入会执行此操作，因此循环不变断言将失败！

So our program will halt there itself. This ensures that we can detect any design flaw in our program, and handle such inputs accordingly.

因此，我们的程序将自行停止。 这确保了我们可以检测到程序中的任何设计缺陷，并相应地处理此类输入。

结论 (Conclusion)

In this article, we learned how we could check for assertions, using the assert macro in C/C++. For similar articles on C, do look at our tutorial section on C programming.

在本文中，我们学习了如何使用C / C ++中的assert宏来检查断言。 有关C的类似文章，请查看我们有关C编程的教程部分。

参考资料 (References)

• Berkeley Guide on using assertions in C/C++Berkeley关于在C / C ++中使用断言的指南

翻译自: https://www.journaldev.com/39002/assert-in-c-plus-plus

断言失败的vc++文档