如何在C ++中获取子字符串并在字符串之间添加字符

Question

I have a string Hello foo how are you.

I want to change it to Hello\\r\\nfoo how are you.

I wanted to know the way to get the substring Hello add \\r\\n in place of space and add all other strings as they are. This is to show the multiline.

EDIT:

We don't know the length of first substring. We would not know how long the first substring will be.

Thanks.

Answer 1

To get a substring your answer lies with the function string::substr :

string::substr (size_t pos = 0, size_t len = npos) const;

1. pos parameter is the index of the first character to be copied as a substring.
2. len parameter is the number of characters to include in the substring starting from the index.

Returns a newly instantiated string object with its value being the substring from the specified string object it was invoked on.

// Example:
#include <iostream>
#include <string>

int main () {
  std::string str1= "Hello Stack Overflow";
  std::string str2 = str.substr (0,5); // "Hello
  std::cout << str2 << std::endl; // Prints "Hello"

  return 0;

}

---

UPDATE: However it looks like different from your title, what you're needing for is to change some characters in between not knowing the substring's length

For that your answer is string::replace :

string& replace (size_t pos,  size_t len,  const string& str);

Replaces the portion of the string that starts at index pos and goes up to index len.

1. pos parameter is the index of the first character to be replaced.
2. len parameter is the number of characters to be replaced starting from the index.
3. str string parameter to replace it with.

---

    // Example
    int main() 
       std::string str = "Hello Stack Overflow.";
       std::string str2 = "good";
       str.replace(6, 4, str2);   // str = "Hello goodStackOverflow"
       return 0;
    }

---

In some compilers you might not need to add it, but you will need to include the string header to make sure your code is portable and maintainable with:

#include <string>

Answer 2

#include <iostream>
#include <string>

int main() {
  std::string s = "Hello foo how are you.";
  s.replace(s.find_first_of(" "),1,"\r\n");
  std::cout << s << std::endl; #OUTPUTS: "Hello
                               #          foo how are you."
  return 0;
}

What you want to use here is the string::replace(pos,len,insert_str); , this function allows you to replace a specified sub-string in s with your "\\r\\n" .

Edit: You want to use s.find_first_of(str) to find the first occurrence of the string " "

Answer 3

Not a complete answer, because this looks like homework, but other approaches you could use include std::find() in <algorithm> and strchr() in <string.h> . If you need to search for any whitespace and not just the ' ' character, you might use std::find_first_of() or strcspn() .

In the future, I'd check out the documentation for: the member functions of std::basic_string , the utility functions in <string> , the functions in <algorithm> , and the functions in <string.h> , as those will generally be the tools you have to work with.