C++ Assert() assertion mechanism principle and usage
MSDN原文如是说：
Evaluates an expression and, when the result is false, prints a diagnostic message and aborts the program.
（判断一个表达式，如果结果为假，输出诊断消息并中止程序。）
void assert( int expression );
参数：Expression (including pointers) that evaluates to nonzero or 0.（表达式【包括指针】是非零或零）
原理：assert的作用是现计算表达式 expression ，如果其值为假（即为0），那么它先向stderr打印一条出错信息，然后通过调用 abort 来终止程序运行。
MSDN示例程序;
// crt_assert.c
// compile with: /c
#include <stdio.h>
#include <assert.h>
#include <string.h>
void analyze_string( char *string ); // Prototype
int main( void )
{
char test1[] = "abc", *test2 = NULL, test3[] = "";
printf ( "Analyzing string '%s'\n", test1 ); fflush( stdout );
analyze_string( test1 );
printf ( "Analyzing string '%s'\n", test2 ); fflush( stdout );
analyze_string( test2 );
printf ( "Analyzing string '%s'\n", test3 ); fflush( stdout );
analyze_string( test3 );
}
// Tests a string to see if it is NULL,
// empty, or longer than 0 characters.
void analyze_string( char * string )
{
assert( string != NULL ); // Cannot be NULL
assert( *string != '\0' ); // Cannot be empty
assert( strlen( string ) > 2 ); // Length must exceed 2
}输出结果
Analyzing string 'abc' Analyzing string '(null)' Assertion failed: string != NULL, file assert.cpp, line 25 abnormal program termination
用法总结：
1)在函数开始处检验传入参数的合法性
如:
int resetBufferSize(int nNewSize)
{
//功能:改变缓冲区大小,
//参数:nNewSize 缓冲区新长度
//返回值:缓冲区当前长度
//说明:保持原信息内容不变 nNewSize<=0表示清除缓冲区
assert(nNewSize >= 0);
assert(nNewSize <= MAX_BUFFER_SIZE);
...
}
2)每个assert只检验一个条件,因为同时检验多个条件时,如果断言失败,无法直观的判断是哪个条件失败
不好: assert(nOffset>=0 && nOffset+nSize<=m_nInfomationSize);
好: assert(nOffset >= 0);
assert(nOffset+nSize <= m_nInfomationSize);
3)不能使用改变环境的语句,因为assert只在DEBUG个生效,如果这么做,会使用程序在真正运行时遇到问题
错误: assert(i++ < 100)
这是因为如果出错，比如在执行之前i=100,那么这条语句就不会执行，那么i++这条命令就没有执行。
正确: assert(i < 100)；
i++;
4)assert和后面的语句应空一行,以形成逻辑和视觉上的一致感
5)有的地方,assert不能代替条件过滤
ASSERT只有在Debug版本中才有效，如果编译为Release版本则被忽略掉。（在C中，ASSERT是宏而不是函数），使用ASSERT“断言”容易在debug时输出程序错误所在。
而assert()的功能类似，它是ANSI C标准中规定的函数，它与ASSERT的一个重要区别是可以用在Release版本中。
使用assert的缺点是，频繁的调用会极大的影响程序的性能，增加额外的开销。
在调试结束后，可以通过在包含#include
#include
#define NDEBUG
#include
加入#define NDEBUG之后，上文第一个例子输出结果为：
Analyzing string 'abc' Analyzing string '(null)' Analyzing string ''
在面试中经常用到的一个题目：
已知memcpy的函数为： void* memcpy(void *dest , const void* src , size_t count)其中dest是目的指针，src是源指针。不调用c++/c的memcpy库函数，请编写memcpy。
void* memcpy(void *dst, const void *src, size_t count)
{
//安全检查
assert( (dst != NULL) && (src != NULL) );
unsigned char *pdst = (unsigned char *)dst;
const unsigned char *psrc = (const unsigned char *)src;
//防止内存重复
assert(!(psrc<=pdst && pdst<psrc+count));
assert(!(pdst<=psrc && psrc<pdst+count));
while(count--)
{
*pdst = *psrc;
pdst++;
psrc++;
}
return dst;
} 以上就是C++ Assert()断言机制原理以及使用的内容，更多相关内容请关注PHP中文网（www.php.cn）！
Hot AI Tools
Undresser.AI Undress
AI-powered app for creating realistic nude photos
AI Clothes Remover
Online AI tool for removing clothes from photos.
Undress AI Tool
Undress images for free
Clothoff.io
AI clothes remover
Video Face Swap
Swap faces in any video effortlessly with our completely free AI face swap tool!
Hot Article
Hot Tools
Notepad++7.3.1
Easy-to-use and free code editor
SublimeText3 Chinese version
Chinese version, very easy to use
Zend Studio 13.0.1
Powerful PHP integrated development environment
Dreamweaver CS6
Visual web development tools
SublimeText3 Mac version
God-level code editing software (SublimeText3)
Hot Topics
1655
14
1413
52
1306
25
1252
29
1226
24
C# vs. C : History, Evolution, and Future Prospects
Apr 19, 2025 am 12:07 AM
The history and evolution of C# and C are unique, and the future prospects are also different. 1.C was invented by BjarneStroustrup in 1983 to introduce object-oriented programming into the C language. Its evolution process includes multiple standardizations, such as C 11 introducing auto keywords and lambda expressions, C 20 introducing concepts and coroutines, and will focus on performance and system-level programming in the future. 2.C# was released by Microsoft in 2000. Combining the advantages of C and Java, its evolution focuses on simplicity and productivity. For example, C#2.0 introduced generics and C#5.0 introduced asynchronous programming, which will focus on developers' productivity and cloud computing in the future.
Where to write code in vscode
Apr 15, 2025 pm 09:54 PM
Writing code in Visual Studio Code (VSCode) is simple and easy to use. Just install VSCode, create a project, select a language, create a file, write code, save and run it. The advantages of VSCode include cross-platform, free and open source, powerful features, rich extensions, and lightweight and fast.
Golang and C : Concurrency vs. Raw Speed
Apr 21, 2025 am 12:16 AM
Golang is better than C in concurrency, while C is better than Golang in raw speed. 1) Golang achieves efficient concurrency through goroutine and channel, which is suitable for handling a large number of concurrent tasks. 2)C Through compiler optimization and standard library, it provides high performance close to hardware, suitable for applications that require extreme optimization.
The Performance Race: Golang vs. C
Apr 16, 2025 am 12:07 AM
Golang and C each have their own advantages in performance competitions: 1) Golang is suitable for high concurrency and rapid development, and 2) C provides higher performance and fine-grained control. The selection should be based on project requirements and team technology stack.
Python vs. C : Learning Curves and Ease of Use
Apr 19, 2025 am 12:20 AM
Python is easier to learn and use, while C is more powerful but complex. 1. Python syntax is concise and suitable for beginners. Dynamic typing and automatic memory management make it easy to use, but may cause runtime errors. 2.C provides low-level control and advanced features, suitable for high-performance applications, but has a high learning threshold and requires manual memory and type safety management.
Golang and C : The Trade-offs in Performance
Apr 17, 2025 am 12:18 AM
The performance differences between Golang and C are mainly reflected in memory management, compilation optimization and runtime efficiency. 1) Golang's garbage collection mechanism is convenient but may affect performance, 2) C's manual memory management and compiler optimization are more efficient in recursive computing.
How to use VSCode
Apr 15, 2025 pm 11:21 PM
Visual Studio Code (VSCode) is a cross-platform, open source and free code editor developed by Microsoft. It is known for its lightweight, scalability and support for a wide range of programming languages. To install VSCode, please visit the official website to download and run the installer. When using VSCode, you can create new projects, edit code, debug code, navigate projects, expand VSCode, and manage settings. VSCode is available for Windows, macOS, and Linux, supports multiple programming languages and provides various extensions through Marketplace. Its advantages include lightweight, scalability, extensive language support, rich features and version
How to execute code with vscode
Apr 15, 2025 pm 09:51 PM
Executing code in VS Code only takes six steps: 1. Open the project; 2. Create and write the code file; 3. Open the terminal; 4. Navigate to the project directory; 5. Execute the code with the appropriate commands; 6. View the output.
