在 C++ 中计算字符串中的字符出现次数
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Count character occurrences in a string in C++
提问by andre de boer
How can I count the number of "_"in a string like "bla_bla_blabla_bla"?
如何计算"_"字符串中的数量"bla_bla_blabla_bla"？
回答by Benoit
#include <algorithm>
std::string s = "a_b_c";
size_t n = std::count(s.begin(), s.end(), '_');
回答by schnaader
Pseudocode:
伪代码：
count = 0
For each character c in string s
Check if c equals '_'
If yes, increase count
EDIT: C++ example code:
编辑：C++ 示例代码：
int count_underscores(string s) {
int count = 0;
for (int i = 0; i < s.size(); i++)
if (s[i] == '_') count++;
return count;
}
Note that this is code to use together with std::string, if you're using char*, replace s.size()with strlen(s).
请注意，这是与 一起使用的代码std::string，如果您使用的是char*，请替换s.size()为strlen(s)。
Also note: I can understand you want something "as small as possible", but I'd suggest you to use this solution instead. As you see you can use a function to encapsulate the code for you so you won't have to write out the forloop everytime, but can just use count_underscores("my_string_")in the rest of your code. Using advanced C++ algorithms is certainly possible here, but I think it's overkill.
另请注意：我可以理解您想要“尽可能小”的东西，但我建议您改用此解决方案。如您所见，您可以使用函数为您封装代码，这样您就不必for每次都写出循环，而可以count_underscores("my_string_")在其余代码中使用。在这里使用高级 C++ 算法当然是可能的，但我认为这太过分了。
回答by Tamás Szelei
Old-fashioned solution with appropriately named variables. This gives the code some spirit.
具有适当命名变量的老式解决方案。这给了代码一些精神。
#include <cstdio>
int _(char*__){int ___=0;while(*__)___='_'==*__++?___+1:___;return ___;}int main(){char*__="_la_blba_bla__bla___";printf("The string \"%s\" contains %d _ characters\n",__,_(__));}
Edit: about 8 years later, looking at this answer I'm ashamed I did this (even though I justified it to myself as a snarky poke at a low-effort question). This is toxic and not OK. I'm not removing the post; I'm adding this apology to help shifting the atmosphere on StackOverflow. So OP: I apologize and I hope you got your homework right despite my trolling and that answers like mine did not discourage you from participating on the site.
编辑：大约 8 年后，看着这个答案，我很惭愧我这样做了（尽管我认为这是对一个轻松问题的尖刻戳戳）。这是有毒的，而且不好。我不会删除帖子；我添加这个道歉是为了帮助改变 StackOverflow 上的气氛。所以 OP：我很抱歉，我希望你的作业做对了，尽管我一直在拖钓，而且像我这样的答案并没有阻止你参与这个网站。
回答by user1977268
#include <boost/range/algorithm/count.hpp>
std::string str = "a_b_c";
int cnt = boost::count(str, '_');
回答by Diego Sevilla
You name it... Lambda version... :)
你的名字... Lambda 版本... :)
using namespace boost::lambda;
std::string s = "a_b_c";
std::cout << std::count_if (s.begin(), s.end(), _1 == '_') << std::endl;
You need several includes... I leave you that as an exercise...
你需要几个包括......我把它留给你作为练习......
回答by Nagappa
Using the lambda function to check the character is "_" then only count will be incremented else not a valid character
使用 lambda 函数检查字符是否为“_”，然后只会增加计数，否则不是有效字符
std::string s = "a_b_c";
size_t count = std::count_if( s.begin(), s.end(), []( char c ){if(c =='_') return true; });
std::cout << "The count of numbers: " << count << std::endl;
std::string s = "a_b_c";
size_t count = std::count_if( s.begin(), s.end(), []( char c ){if(c =='_') return true; });
std::cout << "The count of numbers: " << count << std::endl;
回答by Md. Sakib Hossain
Count character occurrences in a string is easy:
计算字符串中出现的字符很容易：
#include <bits/stdc++.h>
using namespace std;
int main()
{
string s="Sakib Hossain";
int cou=count(s.begin(),s.end(),'a');
cout<<cou;
}
回答by Md. Sakib Hossain
There are several methods of std::string for searching, but find is probably what you're looking for. If you mean a C-style string, then the equivalent is strchr. However, in either case, you can also use a for loop and check each character—the loop is essentially what these two wrap up.
std::string 有多种搜索方法，但 find 可能是您要查找的方法。如果您的意思是 C 风格的字符串，那么等价物是 strchr。然而，在任何一种情况下，您也可以使用 for 循环并检查每个字符——循环本质上是这两个循环的结束。
Once you know how to find the next character given a starting position, you continually advance your search (i.e. use a loop), counting as you go.
一旦您知道如何在给定起始位置的情况下找到下一个字符，您就可以不断推进搜索（即使用循环），边走边数。
回答by Amruta Ghodke
You can find out occurrence of '_' in source string by using string functions. find() function takes 2 arguments , first - string whose occurrences we want to find out and second argument takes starting position.While loop is use to find out occurrence till the end of source string.
您可以使用字符串函数找出源字符串中 '_' 的出现。find() 函数接受 2 个参数，第一个 - 我们想要找出其出现的字符串，第二个参数取起始位置。而循环用于找出直到源字符串末尾的出现。
example:
例子：
string str2 = "_";
string strData = "bla_bla_blabla_bla_";
size_t pos = 0,pos2;
while ((pos = strData.find(str2, pos)) < strData.length())
{
printf("\n%d", pos);
pos += str2.length();
}
回答by Shivam Jha
I would have done this way :
我会这样做：
#include <iostream>
#include <string>
using namespace std;
int main()
{
int count = 0;
string s("Hello_world");
for (int i = 0; i < s.size(); i++)
{
if (s.at(i) == '_')
count++;
}
cout << endl << count;
cin.ignore();
return 0;
}
