Finally began to organize c ++ foundation of the
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1. Output
// C使用printf向终端输出信息
// C++提供了 标准输出流
#include <iostream>
using namespace std;
// 1. c++输出
int time = 8;
cout << "dds:" << time << "点," << "hello world" << endl;
2. function symbol compatible
Most C code can be used directly in C ++, but there are still areas requiring attention.
//如果需要在C++中调用C实现的库中的方法
extern "C" //指示编译器这部分代码使用C的方式进行编译而不是C++
void func(int x, int y);
For funcfunctions are compiled C compiler library function name may be func(no parameter symbol), and the C ++ compiler will produce a similar funciiname or the like.
Therefore, for the C library
#ifdef __cplusplus
extern "C"{
#endif
void func(int x,int y);
#ifdef __cplusplus
}
#endif
//__cplusplus 是由c++编译器定义的宏，用于表示当前处于c++环境
3. references
Reference is C ++ definition of a new type of pointer reference, and two things are needed here to distinguish
//声明形参为引用
void change(int& i) {
i = 10;
}
int i = 1;
change(i);
printf("%d\n",i); //i == 10
4. String
NULL character string is actually using '\0'a one-dimensional array of characters terminated.
//字符数组 = 字符串
char str1[6] = {'H', 'e', 'l', 'l', 'o', '\0'};
//自动加入\0
char str2[] = "Hello";
String Manipulation
| function | description |
|---|---|
| strcpy(s1, s2); | Copy the string to the string s2 s1. |
| strcat(s1, s2); | Connection String s1 s2 to the end of the string. |
| strlen(s1); | It returns the length of the string s1. |
| strcmp(s1, s2); | If s1 and s2 are the same, then return 0; if s1 <s2 is less than 0 is returned; if s1> s2 is greater than 0 is returned |
| strchr(s1, ch); | It returns a pointer to the first occurrence of the character string s1 the location of ch. |
| strstr(s1, s2); | It returns a pointer to the first occurrence of the string s1 s2 string position. |
C ++ string class
C ++ standard library provides a string class type that supports all of the above operations, and also added other more.
#include <string>
//string 定义在 std命令空间中
usning namespace std;
string str1 = "Hello";
string str2 = "World";
str1.append(str2);
//获得c 风格字符串
const char *s1 = str1.c_str();
//字符串长度
str1.size();
//长度是否为0
str1.empty();
......
5. namespace
namespace namespace equivalent package
namespace A{
void a(){}
}
错误 : a();
// :: 域操作符
正确： A::a();
//当然也能够嵌套
namespace A {
namespace B{
void a() {};
}
}
A::B::a();
//还能够使用using 关键字
using namespace A;
using namespace A::B;