String alrotithm described by cpp

Handling string with cpp

IO

从line中间抠出word

 void get_words(vector<string> & vec, char * line){
     int left = 0;
     int right = 0;

     while(line[left] != '\0'){
         while(line[left] != '\0'){
         if(isspace(line[left])) break;
         left ++;
         }
         right = left;
         while(!isspace(line[right])) right ++;
         // not included right
         string word(line + left, line + right);
         // line may maybe end with space
         if(word.size()) vec.push_back(word);
         // find the next word
         left = right;
     }
 }

一行行的读文件

    #include <fstream>
    string line;
    std::ifstream infile("thefile.txt");
    while (std::getline(infile, line)){
        std::istringstream iss(line);
        int a, b;
        if (!(iss >> a >> b)) { break; } // error
    }

字符串中间查找

    find

字符串含有分隔符

http://ysonggit.github.io/coding/2014/12/16/split-a-string-using-c.html

std::string s = "scott>=tiger>=mushroom";
std::string delimiter = ">=";

size_t pos = 0;
std::string token;
while ((pos = s.find(delimiter)) != std::string::npos) {
    token = s.substr(0, pos);
    std::cout << token << std::endl;
    s.erase(0, pos + delimiter.length());
}
std::cout << s << std::endl;

trim

boost::trim()

构造函数

创建相同字母字符串

Cpp String

https://www.fluentcpp.com/2017/04/21/how-to-split-a-string-in-c/

常用函数

stoi
string 是可以改变的
find 字符串包含 int l = str1.find(str2);
char 大小写切换 tolower() toupper() islower isupper
substr() ``` std::string str=”We think in generalities, but we live in details.”; // (quoting Alfred N. Whitehead)

std::string str2 = str.substr (3,5); // “think”

std::size_t pos = str.find(“live”); // position of “live” in str

std::string str3 = str.substr (pos); // get from “live” to the end

std::cout « str2 « ’ ‘ « str3 « ‘\n’;

6. isdigit

## IO
1. fgets()
Reads characters from stream and stores them as a C string into str until (num-1)
characters have been read or either a newline or the end-of-file is reached, whichever happens first.
A newline character makes fgets stop reading, but it is considered a valid character by the function and included in the string copied to str.



2. scanf 读取str 的时候， 前面的空字符必定会被抛弃， 后面的不会处理， 也就是下一次读取的时候继续
## spilt

std::string s = “scott>=tiger>=mushroom”; std::string delimiter = “>=”;

size_t pos = 0; std::string token; while ((pos = s.find(delimiter)) != std::string::npos) { token = s.substr(0, pos); std::cout « token « std::endl; s.erase(0, pos + delimiter.length()); } std::cout « s « std::endl;

## string 和 char[] 的转换
1.

char arr[]; string a(arr)

string temp = “cat”; char tab2[1024]; strcpy(tab2, temp.c_str());

## 初始化String的几种方法

string s;

## 整数 和 string 之间转化
1. to_string
2. stoi atoi
3. \>\> 运算符
4. sscanf


## 来自于 cstring 常用函数
1. strcpy
2. scanf
Any number of non-whitespace characters, stopping at the first whitespace character found. A terminating null character is automatically added at the end of the stored sequence.
3. sscanf
4. getline

## 正则表达式
1. strchr
returns a pointer to the first occurrence of character in the C string str.

## contains

if (s1.find(s2) != std::string::npos) { std::cout « “found!” « ‘\n’; }

## sstream
str(), which returns the contents of its buffer in string type.
str(string), which set the contents of the buffer to the string argument.

## trim and reduce

#include #include

std::string trim(const std::string& str, const std::string& whitespace = “ \t”){ const auto strBegin = str.find_first_not_of(whitespace); if (strBegin == std::string::npos) return “”; // no content

const auto strEnd = str.find_last_not_of(whitespace);
const auto strRange = strEnd - strBegin + 1;

return str.substr(strBegin, strRange); }

std::string reduce(const std::string& str, const std::string& fill = “ “, const std::string& whitespace = “ \t”){ // trim first auto result = trim(str, whitespace);

// replace sub ranges
auto beginSpace = result.find_first_of(whitespace);
while (beginSpace != std::string::npos)
{
    const auto endSpace = result.find_first_not_of(whitespace, beginSpace);
    const auto range = endSpace - beginSpace;

    result.replace(beginSpace, range, fill);

    const auto newStart = beginSpace + fill.length();
    beginSpace = result.find_first_of(whitespace, newStart);
}

return result; }

int main(void){ const std::string foo = “ too much\t \tspace\t\t\t “; const std::string bar = “one\ntwo”;

std::cout << "[" << trim(foo) << "]" << std::endl;
std::cout << "[" << reduce(foo) << "]" << std::endl;
std::cout << "[" << reduce(foo, "-") << "]" << std::endl;

std::cout << "[" << trim(bar) << "]" << std::endl; } ```

MISC

实现对于类对象的排序¹

class MyStruct{
    int key;
    std::string stringValue;

    MyStruct(int k, const std::string& s) : key(k), stringValue(s) {}

    bool operator < (const MyStruct& str) const{
        return (key < str.key);
    }
};
std::sort(vec.begin(), vec.end());

struct MyStruct{
    int key;
    std::string stringValue;

    MyStruct(int k, const std::string& s) : key(k), stringValue(s) {}

    bool operator > (const MyStruct& str) const{
        return (key > str.key);
    }
};
std::sort(vec.begin(), vec.end(),greater<MyStruct>());


bool comp(const ClassOne& lhs, const ClassOne& rhs)
{
  return lhs.valueData < rhs.valueData;
}

std::sort(cone, cone+10, comp);
or, in C++11,

std::sort(std::begin(cone), std::end(cone), comp);


struct MyStruct
{
    int key;
    std::string stringValue;

    MyStruct(int k, const std::string& s) : key(k), stringValue(s) {}
};

struct less_than_key
{
    bool operator() (const MyStruct& struct1, const MyStruct& struct2)
    {
        return (struct1.key < struct2.key);
    }
};
std::sort(vec.begin(), vec.end(), less_than_key());


// 使用 lambda
sort(a.begin(), a.end(),
       [](const MyStruct &struct1, const MyStruct &struct2) -> bool
       {
         return (struct1.key < struct2.key);
       });

总结 : 要么定义为函数，要么定义为 lambda

memset 处理二维数组

priority_queue

和 heap 是什么关系 ?

ques

最快读入的string的方法是什么？

本站所有文章转发 CSDN 将按侵权追究法律责任，其它情况随意。

https://stackoverflow.com/questions/1380463/sorting-a-vector-of-custom-objects ↩