2.using 类内函数指针重命名 [相同类型不同函数，放置到 std::map 中会有用，减少代码量]
#include <iostream>
class c{
public:
using pfunc_type = void(c::*)();
pfunc_type pfunc = nullptr;
c(){ pfunc = &c::up;}
inline void call(){ (this->*pfunc)(); }
private:
int num = 0;
void up(){
++num;
std::cout << num << std::endl;
}
};
int main(){
c *C = new c;
C->call();
delete C;
}
3.指针引用
#include <iostream>
int main(){
int a = 3;
/* 指针引用 */
int * const &p = &a;
*p = 4;
std::cout << a << std::endl;
/* 原始引用 */
int &theA = *p;
theA = 5;
std::cout << a << std::endl;
}
4.tuple使用
#include <iostream>
#include <tuple>
#include <functional>
#include <string>
int main() {
/* 声明时赋值 */
std::tuple<std::string, std::function<void()>> tp("i++", [](){
static int i = 0;
std::cout << i++ << std::endl;
} );
std::cout << "call " << std::get<0>(tp) << std::endl;
std::get<1>(tp)();
/* 先声明，后赋值 */
std::tuple<float, std::string> id2name;
id2name = make_tuple(1.5, std::string("gulou"));
std::cout << "id :" << std::get<0>(id2name) << " name :" << std::get<1>(id2name) << std::endl;
}
5.读取文件到字符串 [遇到 空格/回车 结束]
#include <iostream>
#include <fstream>
#include <string>
inline std::string readUrl( std::string fName="input.txt", std::string result="" ) { std::ifstream os; return os.open(fName), os >> result, os.close(), result; }
int main()
{
std::cout << readUrl();
}
6.call_once 控制调用一次
#include <iostream>
#include <mutex>
/* compile : g++ call_once.cpp -std=c++11 -pthread */
int main(){
std::once_flag flag; /* 如果你的函数操作不会产生异常，那么可以使用std::call_once，使得代码更加的安全简洁易读。 */
unsigned int MAX = 50;
std::call_once(flag, [&MAX ]() { MAX = (MAX == 50) ? (MAX + 2950) : MAX ; } );
std::call_once(flag, [&MAX ]() { MAX = (MAX == 50) ? (MAX + 2950) : MAX ; } );
std::cout << MAX << std::endl; /* output :3000 */
}
7.algorithm 之 find_if 、swap
#include <iostream> /* std::cout */
#include <algorithm> /* std::find_if */
#include <vector> /* std::vector */
/* compile : g++ find_if.cpp -std=c++11 */
int main () {
std::vector<int> vec_i;
vec_i.push_back(10);
vec_i.push_back(55);
vec_i.push_back(25);
/* Returns an iterator to the first element in the range [first,last) for which pred returns true.
If no such element is found, the function returns last. */
auto it = std::find_if (vec_i.begin(), vec_i.end(), [](int &i) { return (i%2) == 1; });
if ( it != vec_i.end() ) {
std::cout << "The first odd value is " << *it << std::endl;
}
std::swap(vec_i[1], vec_i[2]); /* Exchanges the values of a and b. parameters all reference, impl by std::move */
it = std::find_if (vec_i.begin(), vec_i.end(), [](int &i) { return (i%2) == 1; });
if ( it != vec_i.end() ) {
std::cout << "The first odd value is " << *it << std::endl;
}
return 0;
}
8.unique_ptr 示例
std::unique_ptr<AVFrame, void(*)(AVFrame*) > unique_p(av_frame_alloc(), [](AVFrame *ptr){
av_frame_free(&ptr);
});
9.运行时计算 【constexpr 】
#include <iostream>
#include <string>
enum class languageType:int {
CH,
EN,
JAP,
};
static languageType lan = languageType::EN;
constexpr const char* languageName ( const languageType lan) {
return languageType::CH == lan ? "中文": \
languageType::EN == lan ? "English" : \
/* JAP */ "日本語";
}
int main(){
std::cout << languageName (lan) << std::endl;
return 0;
}
---
10.字符串格式化 【string format 】
std::string StringFormat(const char* fmt, ...) {
char buffer[kMaxSize];
va_list args;
va_start(args, fmt);
int result = vsnprintf(buffer, kMaxSize, fmt, args);
va_end(args);
if ( result < 0) { /* error */
std::cout << "String Format Convert Error : " << kMaxSize << " " << result << std::endl;
} else if ( result > kMaxSize ) { /* warning */
std::cout << "String Format Convert Warning : truncated string" << std::endl;
}
return std::string(buffer);
}
/* usage:
std::cout << StringFormat("hello %s","world!") << std::endl;
*/
11.字符串查找最后一个对应字符后的字符串
#include<bits/stdc++.h>
int main(){
std::string s(R"(https://editor.csdn.net/md/?articleId=126165427)");
int ret = s.find_last_of('/');
if (ret != std::string::npos) {
s = s.substr(ret+1, 999);;
std::cout << s << std::endl;
} else {
std::cout << "error" << std::endl;
}
}
/* result:
[root@jn string]# ./a.out
?articleId=126165427
[root@jn string]#*/
12.基于C++11的毫秒计时器类，精度到0.001ms，开箱即用
#include <iostream>
#include <chrono>
#include <thread>
class jnTimer {
public: /* return milliseconds escaped, Precision to 0.001 ms*/
jnTimer(){ update(); }
inline void update() { begin = HrClock::now(); }
inline double diff() { return std::chrono::duration_cast<MicroSeconds>(HrClock::now() - begin).count() / 1e3; }
private:
using HrClock = std::chrono::high_resolution_clock;
using MicroSeconds = std::chrono::microseconds;
HrClock::time_point begin{ MicroSeconds::zero() };
};
/* compile: g++ -std=c++11 timer.cpp */
int main()
{
jnTimer timer; /* timer.update(); */
std::this_thread::sleep_for( std::chrono::milliseconds( 300 ) );/* do your work */
std::cout << "diff:" << timer.diff() << std::endl;
return 0;
}
13.三分钟读完《Essential C++》
见 https://blog.csdn.net/weixin_44328568/article/details/131720185
14.计算字节为对应单位的大小[human-readable]
#include <stdint.h>
#include <cstdlib>
#include <cstdio>
std::string bytesToSize(uint64_t bytes)
{
static const char* suffixes[] = {"B", "KB", "MB", "GB", "TB"};
int i = 0;
double dblBytes = bytes;
while (dblBytes >= 1024 && i < sizeof(suffixes) / sizeof(suffixes[0]) - 1) {
dblBytes /= 1024;
i++;
}
char buffer[32];
snprintf(buffer, sizeof(buffer), "%.2f %s", dblBytes, suffixes[i]);
return std::string(buffer);
}
15.enum与字符串在固定（不修改）数据上的关联操作[代替std::map会更高效]
#include <iostream>
#include <string>
enum Fruit {
APPLE,
BANANA,
CHERRY,
COUNT /* COUNT 用于获取 enum 的项数，始终放在最后 */
};
const std::string FruitNames[COUNT] = {
"Apple",
"Banana",
"Cherry"
};
int main() {
Fruit fruit = BANANA;
std::cout << "Selected fruit: " << FruitNames[fruit] << std::endl;
return 0;
}
