[cpp]: c_string 类的实现(bug)

[cpp]:  c_string 类的实现(bug)

 

 

 

 

一、说明

 

　　1、当每个【c_string对象】到达自身的生命周期时，这个【c_string对象】为什么不调用自身的析构函数【 ~c_string() 】 ？

 

 

 

 

二、源程序

#include  <iostream>
#include  <string>

using namespace std;

#define ENDSTRING '\0'

//  c_string::begin
class c_string
{
private:
int mv_size =  0 ;
char *mv_string = nullptr ;
static int sv_objcounter ;        //  count objects of class c_string

public:
c_string()
{
    mv_size = 0 ;
    mv_string = nullptr  ;
    (c_string::sv_objcounter)++ ;
}

c_string( const char *s )
{
    (c_string::sv_objcounter)++ ;
    
    for ( int i = 0 ;  s[i] != '\0' ;  i++ )
    {
        ++(mv_size) ;
    }

    const int CSIZE = mv_size + 1 ;
    mv_string  =  new char[CSIZE] ;
    if ( mv_string == nullptr )
    {
        cout << "[error]#\t Lack Memory. " << endl ;
        exit (1) ;
    }
    mv_string[CSIZE] = ENDSTRING ;
    
    for ( int j = 0 ;  s[j] != '\0' ;  j++ )
    {
        mv_string[j] = s[j] ;
    }
    mv_string[CSIZE] = ENDSTRING ;
}

~c_string()
{
    mv_size = 0 ;
    delete [] mv_string ;
    //mv_string = nullptr ;
    
    cout <<"[~c_string]#\t" ;
    cout << "obj_num := " << --(c_string::sv_objcounter) ;
    cout << ",  size := " << mv_size ; 
    cout << ",  pt_string := " << mv_string << endl;
}

void mf_set_string( const char *s )
{
    if ( mv_string != nullptr )
    {
        delete mv_string ;
        mv_size  =  0 ;
    }

    for ( int i = 0 ;  s[i] != '\0' ;  i++ )
    {
        ++(mv_size) ;
    }

    const int CSIZE = mv_size + 1 ;
    mv_string  =  new char[CSIZE] ;
    if ( mv_string == nullptr )
    {
        cout << "[error]#\t Lack Memory. " << endl ;
        exit (1) ;
    }
    mv_string[CSIZE] = ENDSTRING ;
    
    for ( int j = 0 ;  s[j] != '\0' ;  j++ )
    {
        mv_string[j] = s[j] ;
    }
    mv_string[CSIZE] = ENDSTRING ;
}

char* mf_get_string()
{
    return mv_string;
}

int mf_get_size()
{
    return mv_size;
}

void mf_out()
{
    cout <<"[c_string]#\t" << mv_string << ",  " << mv_size << endl;
}

};  
int c_string::sv_objcounter = 0 ;
//  c_string::end

void f_char()
{
    char s[] = "helloworld" ;
    cout << "[os]#\t" << "char_output:begin" << endl;
    int size = 0;
    for ( int i=0 ; s[i] != '\0' ; i++ )
    {
        cout << "[os]#\t" << s[i] << endl ;
        ++size ;
    }
    cout << "[os]#\tsize := " << size << endl;
    cout << "[os]#\t" << "char_output:end" << endl;
}

void f_string()
{
    std::string s = "helloworld";
    cout << "[os]#\t" << "string_output:begin" << endl;
    int size = 0;
    for ( int i=0 ; s[i] != '\0' ; i++ )
    {
        cout << "[os]#\t" << s[i] << endl ;
        ++size ;
    }
    cout << "[os]#\tsize := " << size << endl;
    cout << "[os]#\t" << "string_output:end" << endl;    
}

void f_run()
{
    //f_char() ;
    //f_string() ;
    
    c_string s("sun-wukong");
    s.mf_out();
    
    c_string z("zhu-wujing");
    //c_string z{"zhu-wujing"};
    z.mf_out();
    
    c_string t;
    t.mf_set_string("tang-xuanzang");
    t.mf_out();
}

// test part
int main()
{
    f_run() ;
    return 0 ;
}

 

 

 

三、运行

g++ -std=c++20 -O2 -Wall -pedantic -pthread main.cpp && ./a.out


[c_string]#    sun-wukong,  10
[c_string]#    zhu-wujing,  10
[c_string]#    tang-xuanzang,  13
[~c_string]#    obj_num := 2,  size := 0,  pt_string := 
[~c_string]#    obj_num := 1,  size := 0,  pt_string := `
[~c_string]#    obj_num := 0,  size := 0,  pt_string := @

 

 

 

四、参考资料：

 

　　1、　　nullptr, the pointer literal (since C++11)　　--　　https://en.cppreference.com/w/cpp/language/nullptr