[C++知识库]char*引发的一些错误

首先了解一下char* 和 char[]区别，

这篇文章【C/C++】对char* 和 char[]区别的一些理解

https://blog.csdn.net/u012611878/article/details/78291036写的很好，推荐看看。

在VS2019中，原来错误的代码

#include <iostream>

class Student 
{
private:
	int m_number;
	char* m_name;
public:
	Student(int number,const char* name);//构造函数
	Student(const Student &s);//拷贝构造函数
	void show();
	void setNumber(int number);
	void setName(char* name);
};

Student::Student(int number,char* name)
{
	m_number = number;
	m_name = new char[strlen(name) + 1]; //申请内存
	strcpy(m_name, name);
}
Student::Student(const Student &s)
{
	m_number = s.m_number;
	m_name = new char[strlen(s.m_name) + 1]; //申请内存
	strcpy(m_name, s.m_name);
}

void Student::setNumber(int number)
{
	m_number = number;
}

void Student::setName(char* name)
{
	if (m_name != nullptr)
	{
		delete []m_name;
		m_name = new char[strlen(name) + 1];
		strcpy(m_name, name);

	}
}

void Student::show()
{
	std::cout << "学号：" << m_number << "\t" << "姓名：" << m_name << std::endl;
}

int main()
{
	Student s1(20210001,"张三");
	s1.setName("张小三");
	s1.show();
	return 0;
}

报错1:
E0289 没有与参数列表匹配的构造函数 “Student::Student” 实例

错误分析：

张三这个字符串为const char [5] 类型，而类中的构造函数不同。
解决方法：
将 char * name 改写为const char* name

报错2:
error C4996: ‘strcpy’: This function or variable may be unsafe. Consider using strcpy_s instead. To disable deprecation, use _CRT_SECURE_NO_WARNINGS. See online help for details.错误分析：使用VS2005以上版本（VS2008、VS2010、VS2013、VS2015、VS2017、VS2019）编译在其他编译器下正常通过的C语言程序都有可能遇到。
这种微软的警告，主要因为那些C库的函数，很多函数内部是不进行参数检测的（包括越界类的），微软担心使用这些会造成内存异常，所以就改写了同样功能的函数，改写了的函数进行了参数的检测，使用这些新的函数会更安全和便捷。库函数改写例子：
mkdir改写为 _mkdir
fopen改写为 fopen_s
stricmp改写为 stricmp_s
strcpy改写为strcpy_s
scanf改写为scanf_s

解决方法1：
找到【项目属性】，点击【C/C++】里的【预处理器】，对【预处理器】进行编辑，在里面加入一段代码：_CRT_SECURE_NO_WARNINGS。

修改后：

#define _CRT_SECURE_NO_WARNINGS
#include <iostream>

class Student 
{
private:
	int m_number;
	char* m_name;
public:
	Student(int number,const char* name);
	Student(const Student &s);
	void show();
	void setNumber(int number);
	void setName(const char* name);
};

Student::Student(int number,const char* name)
{
	m_number = number;
	m_name = new char[strlen(name) + 1]; //申请内存
	strcpy(m_name, name);
}

Student::Student(const Student &s)
{
	m_number = s.m_number;
	m_name = new char[strlen(s.m_name) + 1]; //申请内存
	strcpy(m_name, s.m_name);
}

void Student::setNumber(int number)
{
	m_number = number;
}

void Student::setName(const char* name)
{
	if (m_name != nullptr)
	{
		delete []m_name;
		m_name = new char[strlen(name) + 1];
		strcpy(m_name, name);

	}
}

void Student::show()
{
	std::cout << "学号：" << m_number << "\t" << "姓名：" << m_name << std::endl;
}

int main()
{
	Student s1(20210001,"张三");
	s1.setName("张小三");
	s1.show();
	return 0;
}

解决方法2：
根据报错提示，用strcpy_s替代strcpy。

#include <iostream>
#include <string>

class Student 
{
private:
	int m_number;
	char* m_name;
public:
	Student(int number,const char* name);
	Student(const Student &s);
	void show();
	void setNumber(int number);
	void setName(const char* name);
};

Student::Student(int number,const char* name)
{
	m_number = number;
	m_name = new char[strlen(name) + 1]; //申请内存
	strcpy_s(m_name, strlen(name) + 1, name);
}

Student::Student(const Student &s)
{
	m_number = s.m_number;
	m_name = new char[strlen(s.m_name) + 1]; //申请内存
	strcpy_s(m_name, strlen(s.m_name) + 1, s.m_name);
}

void Student::setNumber(int number)
{
	m_number = number;
}

void Student::setName(const char* name)
{
	if (m_name != nullptr)
	{
		delete []m_name;
		m_name = new char[strlen(name) + 1];
		strcpy_s(m_name, strlen(name) + 1, name);

	}
}

void Student::show()
{
	std::cout << "学号：" << m_number << "\t" << "姓名：" << m_name << std::endl;
}

int main()
{
	Student s1(20210001,"张三");
	s1.setName("张小三");
	s1.show();
	return 0;
}

结果：

学号：20210001  姓名：张小三

参考网站：
https://blog.csdn.net/u012611878/article/details/78291036
https://blog.csdn.net/weixin_41529093/article/details/102710192
https://blog.csdn.net/cyrilcloud/article/details/115337480