The essence of C and C ++ code: Reading Notes and Code Reading Notes

The essence of C and C ++ code: Reading Notes and Code Reading Notes

I recently read <C and C ++ code essence>, designed C ++ pointers, exception handling, and other aspects, some of which I think are very good code, it is worth learning from in the work.

1. pointer to a member function

A

#include<iostream>using namespace std;class C{    public:void f(){ cout<<"C::f\n";}void g(){cout<<"C::g\n";}};int main(){C c;void (C::*pmf)()=&C::f;(c.*pmf)();pmf=&C::g;(c.*pmf)();}

B

#include<iostream>using namespace std;class Object{public:    void retrieve(){        cout<<"Object::retrieve"<<endl;    }    void insert(){        cout<<"Object::insert"<<endl;    }    void update(){        cout<<"Object::update"<<endl;    }    void process(int choice);private:    typedef void (Object::*Omf)();    static Omf farray[3];};Object::Omf Object::farray[3]={&Object::retrieve,&Object::insert,&Object::update};void Object::process(int choice){    if(0<=choice && choice<=2)        (this->*farray[choice])();}int show_menu(){    cout<<"1. retrieve\n";    cout<<"2. insert\n";    cout<<"3. update\n";    cout<<"4. quit\n";    cout<<"Please input a num\n";    int n;    cin>>n;    return n;}int main(){    int show_menu();         Object o;      for(;;){        int choice=show_menu();        if(1<=choice && choice<=3)            o.process(choice-1);        else if(choice==4)            break;    }    return 0;}

2. Implement your own assert macro

//assert.h#ifndef ASSERT_H#define ASSERT_Hextern void _assert(char*, char*, long);#define assert(cond) \((cond) \? (void) 0 \: _assert(#cond, __FILE__, __LINE__))#endif

Define your own _ assert method in the c file to conveniently use your own assert macro:

#include <stdio.h>#include <stdlib.h>#include "assert.h"void _assert(char* cond, char* fname, long lineno){fprintf(stderr, "Assertion failed: %s, file %s, line %ld\n", cond, fname, lineno);abort();}int main(){assert(3>4);return 0;}

3. Use setjmp to define a super redirect for Exception Handling

#include <stdio.h>#include <setjmp.h>jmp_buf jumper;void exception();int  deal_exception();main(){     int value = 0;     int i = 0;     value = setjmp(jumper);     if ( 0 == value ) {         exception();     }     else {         switch ( value )         {            case 1:                printf( "solve exception[%d]\n",value );                break;            case 2:                printf( "solve exception[%d]\n",value );                break;            case 3:                printf( "solve exception[%d]\n",value );                break;           default:                printf( "solve exception[%d]\n",value );                break;        }    }}void exception(){    int _err_no = 3;    if ( _err_no == 3 ) {        printf("exception[%d]\n",_err_no);        longjmp(jumper,_err_no);    }    return;}

4. Special Function Template

#include <iostream>#include <string.h>#include <string>using namespace std;template<class T>size_t bytes( T& t){cout<<"(using primary template)\n";return sizeof t;}size_t bytes( char*& t){cout<<"(using char* overload)\n";return sizeof t;}template<>size_t bytes<wchar_t*>( wchar_t*& t){cout<<"(using wchar_t* specialization)\n";return sizeof 2*(wcslen(t)+1);}template<>size_t bytes<>( string& s){cout<<"(using string explicit specialization)\n";return sizeof s;}template<>size_t bytes<float>( float& s){cout<<"(using float explicit specialization)\n";return sizeof s;}int main(){int i;cout<<"bytes in i:"<<bytes(i)<<endl;const char* s="Hello";cout<<"bytes in s:"<<bytes(s)<<endl;const wchar_t* w = (wchar_t*)"goodbye";cout<<"bytes in w:"<<bytes(w)<<endl;string t;cout<<"bytes in t:"<<bytes(t)<<endl;float f;cout<<"bytes in f:"<<bytes(f)<<endl;double d;cout<<"bytes in d:"<<bytes(d)<<endl;return 0;}

Class template Specialization

#include <iostream>using namespace std;template<class T, class U>class A{public:A(){cout<<"Primary template\n";}};template<class T, class U>class A<T*, U>{public:A(){cout <<"<T*,U> partial specialization\n";}};template<class T>class A<T, T>{public:A(){cout <<"<T,T> partial specialization\n";}};template<class U>class A<int, U>{public:A(){cout <<"<int,U> partial specialization\n";}};int main(){A<char,int> a1;A<char*,int> a2;A<float,float> a3;A<int, float> a4;return 0;}

5. How to change data members in constant member functions
A: this pointer is non-constant; B: mutable

#include <iostream>using namespace std;class B{public:    B() {state =0;pos=0;}    void f() const;    void p() {cout<<"state= "<<state<<" pos= "<<pos<<endl;}private:    int state;    mutable int pos;};void B::f() const{    // ((B*)this)->state=1;    const_cast<B*>(this)->state=1;    pos = 1;}int main(){    B b;    b.p();    b.f();    b.p();    return 0;}

6. Signal

#include <stdio.h>#include <signal.h>void ctrlc_handler(int sig);volatile sig_atomic_t ccount = 0;int main(){char buf[100];if(signal(SIGINT, ctrlc_handler) == SIG_ERR){fputs("Error installing ctrlc handler\n", stderr);}while(gets(buf)){puts(buf);}signal(SIGINT, SIG_DFL);printf("You pressed ctrlc %d times\n", ccount);return 0;}void ctrlc_handler(int sig){signal(sig, ctrlc_handler);++ccount;return;}

7. Exception Handling: resource allocation is the initialization Principle

/*exception:logic_errordomain_errorinvalid_argumentlength_errorout_of_rangeruntime_errorrange_erroroverflow_errorunderflow_errorbad_allocbad_castbad_exceptionbad_typeid*/#include <cstdio>#include <memory>using namespace std;class File{    FILE* f;public:    File(const char* fname, const char* mode)    {        f = fopen(fname,mode);        if(!f)            throw 1;    }    ~File()    {        if(f)        {            fclose(f);            puts("File closed");        }    }};int main(){    void f(const char*);    try    {        //f("file0.txt");        f("file1.txt");    }    catch(int x)    {        printf("Caught exception:%d\n", x);    }    return 0;}void f(const char* fname){    auto_ptr<File> xp(new File(fname,"r"));    puts("Processing file...");    throw 2;}

8. Non-standard template library container

#include <valarray>#include <iostream>#include <algorithm>//#include <boost/foreach.hpp>using namespace std;void print(double i){    cout << i <<" ";}int main(){const int N = 10;const double values[N] = {0,1,2,3,4,5,6,7,8,9};const valarray<double> v1(values,N);//for_each(&values[0], &values[9], ptr_fun(print));/*BOOST_FOREACH(double d, values){cout<< d << endl;} */for_each(&v1[0], &v1[10], ptr_fun(print));cout<<endl;cout << "min: "<<v1.min()<<endl;cout << "max: "<<v1.max()<<endl;cout << "sum: "<<v1.sum()<<endl;return 0;}

9 handle memory allocation exceptions

A try {} catch (const bad_alloc & x)

B set_new_handler

#include <iostream>#include <stdlib.h>using namespace std;inline void my_handler(){cout << "Memory exhausted" <<endl;abort();}int main(){set_new_handler(my_handler);for(int i=0;;++i){(void) new double[100];if((i+1) % 10 == 0)cout << (i+1) << " allocations" <<endl;}return 0;}

10. Never run 9 On your computer!