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

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