C++ 检查字符串是否包含C++;
我有一个类型为C++ 检查字符串是否包含C++;,c++,string,substring,C++,String,Substring,我有一个类型为std::string的变量。我想检查它是否包含某个std::string。我该怎么做 是否有一个函数,如果找到字符串,则返回true;如果找不到字符串,则返回false?使用如下方法: if (s1.find(s2) != std::string::npos) { std::cout << "found!" << '\n'; } if(s1.find(s2)!=std::string::npos){ std::cout您可以尝试使用以下函数: s
std::string
的变量。我想检查它是否包含某个std::string
。我该怎么做
是否有一个函数,如果找到字符串,则返回true;如果找不到字符串,则返回false?使用如下方法:
if (s1.find(s2) != std::string::npos) {
std::cout << "found!" << '\n';
}
if(s1.find(s2)!=std::string::npos){
std::cout您可以尝试使用以下函数:
string str ("There are two needles in this haystack.");
string str2 ("needle");
if (str.find(str2) != string::npos) {
//.. found.
}
实际上,您可以尝试使用boost库,我认为std::string没有提供足够的方法来执行所有常见的字符串操作。在boost中,您可以使用:
#包括
#包括
int main(){
std::字符串s(“耿家文”);
std::字符串t(“geng”);
bool b=boost::algorithm::contains(s,t);
你可以试试这个
string s1 = "Hello";
string s2 = "el";
if(strstr(s1.c_str(),s2.c_str()))
{
cout << " S1 Contains S2";
}
string s1=“你好”;
字符串s2=“el”;
if(strstrstr(s1.c_str(),s2.c_str())
{
cout如果您不想使用标准库函数,下面是一个解决方案
#include <iostream>
#include <string>
bool CheckSubstring(std::string firstString, std::string secondString){
if(secondString.size() > firstString.size())
return false;
for (int i = 0; i < firstString.size(); i++){
int j = 0;
// If the first characters match
if(firstString[i] == secondString[j]){
int k = i;
while (firstString[i] == secondString[j] && j < secondString.size()){
j++;
i++;
}
if (j == secondString.size())
return true;
else // Re-initialize i to its original value
i = k;
}
}
return false;
}
int main(){
std::string firstString, secondString;
std::cout << "Enter first string:";
std::getline(std::cin, firstString);
std::cout << "Enter second string:";
std::getline(std::cin, secondString);
if(CheckSubstring(firstString, secondString))
std::cout << "Second string is a substring of the frist string.\n";
else
std::cout << "Second string is not a substring of the first string.\n";
return 0;
}
#包括
#包括
bool CheckSubstring(std::string firstString,std::string secondString){
if(secondString.size()>firstString.size())
返回false;
对于(int i=0;i 这是一个简单的函数
bool find(string line, string sWord)
{
bool flag = false;
int index = 0, i, helper = 0;
for (i = 0; i < line.size(); i++)
{
if (sWord.at(index) == line.at(i))
{
if (flag == false)
{
flag = true;
helper = i;
}
index++;
}
else
{
flag = false;
index = 0;
}
if (index == sWord.size())
{
break;
}
}
if ((i+1-helper) == index)
{
return true;
}
return false;
}
bool-find(弦线、弦剑)
{
布尔标志=假;
int-index=0,i,helper=0;
对于(i=0;i
#包括//标准::搜索
#包括
使用std::search;使用std::count;使用std::string;
int main(){
string mystring=“大海捞针”;
string str=“针”;
string::const_迭代器it;
它=搜索(mystring.begin(),mystring.end(),
str.begin(),str.end())!=mystring.end();
//如果找到字符串…将迭代器返回到mystring中str的第一个元素
//如果找不到字符串…将迭代器返回给mystring.end()
if(it!=mystring.end())
//找到字符串
其他的
//找不到
返回0;
}
从这个网站上的众多答案中,我没有找到一个明确的答案,所以在5-10分钟内,我自己找到了答案。
但这可以在两种情况下实现:
知道在字符串中搜索的子字符串的位置
要么你不知道这个位置,一个字符一个字符地搜索它
>让我们假设在字符串“ABCDE”中搜索子字符串“CD”,我们使用C++中的最简单的子字符串内置函数
对于1:
#include <iostream>
#include <string>
using namespace std;
int i;
int main()
{
string a = "abcde";
string b = a.substr(2,2); // 2 will be c. Why? because we start counting from 0 in a string, not from 1.
cout << "substring of a is: " << b << endl;
return 0;
}
#include <iostream>
#include <string>
using namespace std;
int i;
int main()
{
string a = "abcde";
for (i=0;i<a.length(); i++)
{
if (a.substr(i,2) == "cd")
{
cout << "substring of a is: " << a.substr(i,2) << endl; // i will iterate from 0 to 5 and will display the substring only when the condition is fullfilled
}
}
return 0;
}
#包括
#包括
使用名称空间std;
int i;
int main()
{
字符串a=“abcde”;
字符串b=a.substr(2,2);//2将是c。为什么?因为我们从字符串中的0开始计数,而不是从1开始。
cout您还可以使用系统名称空间。
然后可以使用contains方法
#include <iostream>
using namespace System;
int main(){
String ^ wholeString = "My name is Malindu";
if(wholeString->ToLower()->Contains("malindu")){
std::cout<<"Found";
}
else{
std::cout<<"Not Found";
}
}
#包括
使用名称空间系统;
int main(){
String^whistring=“我的名字是Malindu”;
如果(整体字符串->ToLower()->包含(“malindu”)){
我们可以用这个方法代替。
只是我项目中的一个例子。
参考代码。
还包括一些额外费用
注意if语句
/*
Every C++ program should have an entry point. Usually, this is the main function.
Every C++ Statement ends with a ';' (semi-colon)
But, pre-processor statements do not have ';'s at end.
Also, every console program can be ended using "cin.get();" statement, so that the console won't exit instantly.
*/
#include <string>
#include <bits/stdc++.h> //Can Use instead of iostream. Also should be included to use the transform function.
using namespace std;
int main(){ //The main function. This runs first in every program.
string input;
while(input!="exit"){
cin>>input;
transform(input.begin(),input.end(),input.begin(),::tolower); //Converts to lowercase.
if(input.find("name") != std::string::npos){ //Gets a boolean value regarding the availability of the said text.
cout<<"My Name is AI \n";
}
if(input.find("age") != std::string::npos){
cout<<"My Age is 2 minutes \n";
}
}
}
/*
每一个C++程序都应该有一个入口点。通常,这是主要功能。
每个C++语句以“;”(半冒号)结尾。
但是,预处理器语句的末尾没有“;”。
此外,每个控制台程序都可以使用“cin.get();”语句结束,这样控制台就不会立即退出。
*/
#包括
#include//可以代替iostream使用。还应包括以使用转换函数。
使用名称空间std;
int main(){//主函数。它在每个程序中首先运行。
字符串输入;
while(输入!=“退出”){
cin>>输入;
转换(input.begin(),input.end(),input.begin(),::tolower);//转换为小写。
if(input.find(“name”)!=std::string::npos){//获取有关所述文本可用性的布尔值。
cout如果功能对您的系统至关重要,那么使用旧的strstrstr
方法实际上是有益的。algorithm
中的std::search
方法可能是最慢的。我想创建这些迭代器可能需要很多时间
我用来给整件事计时的代码是
#include <string>
#include <cstring>
#include <iostream>
#include <algorithm>
#include <random>
#include <chrono>
std::string randomString( size_t len );
int main(int argc, char* argv[])
{
using namespace std::chrono;
const size_t haystacksCount = 200000;
std::string haystacks[haystacksCount];
std::string needle = "hello";
bool sink = true;
high_resolution_clock::time_point start, end;
duration<double> timespan;
int sizes[10] = { 10, 20, 40, 80, 160, 320, 640, 1280, 5120, 10240 };
for(int s=0; s<10; ++s)
{
std::cout << std::endl << "Generating " << haystacksCount << " random haystacks of size " << sizes[s] << std::endl;
for(size_t i=0; i<haystacksCount; ++i)
{
haystacks[i] = randomString(sizes[s]);
}
std::cout << "Starting std::string.find approach" << std::endl;
start = high_resolution_clock::now();
for(size_t i=0; i<haystacksCount; ++i)
{
if(haystacks[i].find(needle) != std::string::npos)
{
sink = !sink; // useless action
}
}
end = high_resolution_clock::now();
timespan = duration_cast<duration<double>>(end-start);
std::cout << "Processing of " << haystacksCount << " elements took " << timespan.count() << " seconds." << std::endl;
std::cout << "Starting strstr approach" << std::endl;
start = high_resolution_clock::now();
for(size_t i=0; i<haystacksCount; ++i)
{
if(strstr(haystacks[i].c_str(), needle.c_str()))
{
sink = !sink; // useless action
}
}
end = high_resolution_clock::now();
timespan = duration_cast<duration<double>>(end-start);
std::cout << "Processing of " << haystacksCount << " elements took " << timespan.count() << " seconds." << std::endl;
std::cout << "Starting std::search approach" << std::endl;
start = high_resolution_clock::now();
for(size_t i=0; i<haystacksCount; ++i)
{
if(std::search(haystacks[i].begin(), haystacks[i].end(), needle.begin(), needle.end()) != haystacks[i].end())
{
sink = !sink; // useless action
}
}
end = high_resolution_clock::now();
timespan = duration_cast<duration<double>>(end-start);
std::cout << "Processing of " << haystacksCount << " elements took " << timespan.count() << " seconds." << std::endl;
}
return 0;
}
std::string randomString( size_t len)
{
static const char charset[] = "abcdefghijklmnopqrstuvwxyz";
static const int charsetLen = sizeof(charset) - 1;
static std::default_random_engine rng(std::random_device{}());
static std::uniform_int_distribution<> dist(0, charsetLen);
auto randChar = [charset, &dist, &rng]() -> char
{
return charset[ dist(rng) ];
};
std::string result(len, 0);
std::generate_n(result.begin(), len, randChar);
return result;
}
如果字符串的大小相对较大(数百字节或更多),并且c++17可用,则可能需要使用Boyer Moore Horspool searcher(来自cppreference.com的示例):
#包括
#包括
#包括
#包括
int main()
{
std::string in=“Lorem ipsum door sit amet,concertetur adipising elit,”
“临时性劳动和重大事故”;
std::string needle=“pisci”;
auto it=std::search(in.begin()、in.end(),
标准::博伊尔摩尔搜索器(
针。开始(),针。结束();
if(it!=in.end())
std::cout从C++23开始,您可以使用
#包括
const auto haystack=std::string(“带针的草垛”);
常量自动指针=标准::字符串(“nee
/*
Every C++ program should have an entry point. Usually, this is the main function.
Every C++ Statement ends with a ';' (semi-colon)
But, pre-processor statements do not have ';'s at end.
Also, every console program can be ended using "cin.get();" statement, so that the console won't exit instantly.
*/
#include <string>
#include <bits/stdc++.h> //Can Use instead of iostream. Also should be included to use the transform function.
using namespace std;
int main(){ //The main function. This runs first in every program.
string input;
while(input!="exit"){
cin>>input;
transform(input.begin(),input.end(),input.begin(),::tolower); //Converts to lowercase.
if(input.find("name") != std::string::npos){ //Gets a boolean value regarding the availability of the said text.
cout<<"My Name is AI \n";
}
if(input.find("age") != std::string::npos){
cout<<"My Age is 2 minutes \n";
}
}
}
#include <string>
#include <cstring>
#include <iostream>
#include <algorithm>
#include <random>
#include <chrono>
std::string randomString( size_t len );
int main(int argc, char* argv[])
{
using namespace std::chrono;
const size_t haystacksCount = 200000;
std::string haystacks[haystacksCount];
std::string needle = "hello";
bool sink = true;
high_resolution_clock::time_point start, end;
duration<double> timespan;
int sizes[10] = { 10, 20, 40, 80, 160, 320, 640, 1280, 5120, 10240 };
for(int s=0; s<10; ++s)
{
std::cout << std::endl << "Generating " << haystacksCount << " random haystacks of size " << sizes[s] << std::endl;
for(size_t i=0; i<haystacksCount; ++i)
{
haystacks[i] = randomString(sizes[s]);
}
std::cout << "Starting std::string.find approach" << std::endl;
start = high_resolution_clock::now();
for(size_t i=0; i<haystacksCount; ++i)
{
if(haystacks[i].find(needle) != std::string::npos)
{
sink = !sink; // useless action
}
}
end = high_resolution_clock::now();
timespan = duration_cast<duration<double>>(end-start);
std::cout << "Processing of " << haystacksCount << " elements took " << timespan.count() << " seconds." << std::endl;
std::cout << "Starting strstr approach" << std::endl;
start = high_resolution_clock::now();
for(size_t i=0; i<haystacksCount; ++i)
{
if(strstr(haystacks[i].c_str(), needle.c_str()))
{
sink = !sink; // useless action
}
}
end = high_resolution_clock::now();
timespan = duration_cast<duration<double>>(end-start);
std::cout << "Processing of " << haystacksCount << " elements took " << timespan.count() << " seconds." << std::endl;
std::cout << "Starting std::search approach" << std::endl;
start = high_resolution_clock::now();
for(size_t i=0; i<haystacksCount; ++i)
{
if(std::search(haystacks[i].begin(), haystacks[i].end(), needle.begin(), needle.end()) != haystacks[i].end())
{
sink = !sink; // useless action
}
}
end = high_resolution_clock::now();
timespan = duration_cast<duration<double>>(end-start);
std::cout << "Processing of " << haystacksCount << " elements took " << timespan.count() << " seconds." << std::endl;
}
return 0;
}
std::string randomString( size_t len)
{
static const char charset[] = "abcdefghijklmnopqrstuvwxyz";
static const int charsetLen = sizeof(charset) - 1;
static std::default_random_engine rng(std::random_device{}());
static std::uniform_int_distribution<> dist(0, charsetLen);
auto randChar = [charset, &dist, &rng]() -> char
{
return charset[ dist(rng) ];
};
std::string result(len, 0);
std::generate_n(result.begin(), len, randChar);
return result;
}
Generating 200000 random haystacks of size 10
Starting std::string.find approach
Processing of 200000 elements took 0.00358503 seconds.
Starting strstr approach
Processing of 200000 elements took 0.0022727 seconds.
Starting std::search approach
Processing of 200000 elements took 0.0346258 seconds.
Generating 200000 random haystacks of size 20
Starting std::string.find approach
Processing of 200000 elements took 0.00480959 seconds.
Starting strstr approach
Processing of 200000 elements took 0.00236199 seconds.
Starting std::search approach
Processing of 200000 elements took 0.0586416 seconds.
Generating 200000 random haystacks of size 40
Starting std::string.find approach
Processing of 200000 elements took 0.0082571 seconds.
Starting strstr approach
Processing of 200000 elements took 0.00341435 seconds.
Starting std::search approach
Processing of 200000 elements took 0.0952996 seconds.
Generating 200000 random haystacks of size 80
Starting std::string.find approach
Processing of 200000 elements took 0.0148288 seconds.
Starting strstr approach
Processing of 200000 elements took 0.00399263 seconds.
Starting std::search approach
Processing of 200000 elements took 0.175945 seconds.
Generating 200000 random haystacks of size 160
Starting std::string.find approach
Processing of 200000 elements took 0.0293496 seconds.
Starting strstr approach
Processing of 200000 elements took 0.00504251 seconds.
Starting std::search approach
Processing of 200000 elements took 0.343452 seconds.
Generating 200000 random haystacks of size 320
Starting std::string.find approach
Processing of 200000 elements took 0.0522893 seconds.
Starting strstr approach
Processing of 200000 elements took 0.00850485 seconds.
Starting std::search approach
Processing of 200000 elements took 0.64133 seconds.
Generating 200000 random haystacks of size 640
Starting std::string.find approach
Processing of 200000 elements took 0.102082 seconds.
Starting strstr approach
Processing of 200000 elements took 0.00925799 seconds.
Starting std::search approach
Processing of 200000 elements took 1.26321 seconds.
Generating 200000 random haystacks of size 1280
Starting std::string.find approach
Processing of 200000 elements took 0.208057 seconds.
Starting strstr approach
Processing of 200000 elements took 0.0105039 seconds.
Starting std::search approach
Processing of 200000 elements took 2.57404 seconds.
Generating 200000 random haystacks of size 5120
Starting std::string.find approach
Processing of 200000 elements took 0.798496 seconds.
Starting strstr approach
Processing of 200000 elements took 0.0137969 seconds.
Starting std::search approach
Processing of 200000 elements took 10.3573 seconds.
Generating 200000 random haystacks of size 10240
Starting std::string.find approach
Processing of 200000 elements took 1.58171 seconds.
Starting strstr approach
Processing of 200000 elements took 0.0143111 seconds.
Starting std::search approach
Processing of 200000 elements took 20.4163 seconds.
#include <iostream>
#include <string>
#include <algorithm>
#include <functional>
int main()
{
std::string in = "Lorem ipsum dolor sit amet, consectetur adipiscing elit,"
" sed do eiusmod tempor incididunt ut labore et dolore magna aliqua";
std::string needle = "pisci";
auto it = std::search(in.begin(), in.end(),
std::boyer_moore_searcher(
needle.begin(), needle.end()));
if(it != in.end())
std::cout << "The string " << needle << " found at offset "
<< it - in.begin() << '\n';
else
std::cout << "The string " << needle << " not found\n";
}
#include <string>
const auto haystack = std::string("haystack with needles");
const auto needle = std::string("needle");
if (haystack.contains(needle))
{
// found!
}