最近看了<<C和C++代码精粹>>, 设计到C++的指针，异常处理等方方面面，其中有些自认为非常不错的代码，在工作中非常值得借鉴。
1.指向成员函数的指针
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.实现自己的assert宏
//assert.h #ifndef ASSERT_H #define ASSERT_H extern void _assert(char*, char*, long); #define assert(cond) ((cond) ? (void) 0 : _assert(#cond, __FILE__, __LINE__)) #endif
在c文件中定义自己的_assert方法，就可以方便的使用自己的assert宏了：
#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.使用setjmp定义超级转向来进行异常处理
#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. 函数模板特化
#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;
}
类模板特化
#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.常量成员函数中改变数据成员的方法
A ：this 指针去常量性；B：使用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. 信号
#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.异常处理：资源分配即初始化原则
/*
exception:
logic_error
domain_error
invalid_argument
length_error
out_of_range
runtime_error
range_error
overflow_error
underflow_error
bad_alloc
bad_cast
bad_exception
bad_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. 非标准模板库容器
#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 处理内存分配异常
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!
时间： 2025-02-01 08:57:50