How to trim off whitespace ??

[kalki]

How to trim off white space and string except string which is expected??

str ="This is an example sentence."
str1 ="an".
I just want to print "an" in given string . Given string may change everytime just i want to match it with expected string . Below is my code which is giving output but i know its not right way. Guidence would be helpful to optimize my code.

#include <iostream>
#include <string>

int main () {
  std::string str= "This is an example sentence.";
  std::string str1="an";
  std::size_t found = str.find(str1);
	cout<<found<<'\n';
	int j=found-6;
  string str2 = str.substr (found,(j));

  cout<<str2<<'\n'; // output: 12

  return 0;
}

[coder777]

What are you trying to do?

str2 will contain exactly the same as str1. So why the hassle to find str2?

What whitespaces do you want to trim?

[kalki]

std::string str= "This is an example sentence.";
std::string str1="an";
Comparing these two string , if str1 content i.e "an" present in str, then only print "an" from str earase ramaining string and whitespace from str. This what i intend to do in my code. Am i doing it in right way???

[JLBorges]

std::regex_replace() http://en.cppreference.com/w/cpp/regex/regex_replace

#include <iostream>
#include <regex>
#include <string>

std::string replace_word( std::string str, std::string word, std::string replacement = " " )
{
    // zero or more white space, word boundary, word, word boundary, zero or more white space
    std::regex word_re( "\\s*\\b" + word + "\\b\\s*" ) ;
    return std::regex_replace( str, word_re, replacement ) ;
}

int main()
{
   std::string str = "I know. You know I know. I know you know I know. "
                     "We know Henry knows, and Henry knows we know. "
                     "We're a knowledgeable family." ;

   std::cout << str << '\n'
             << replace_word( str, "know" ) << '\n'
             << replace_word( str, "know(s?)" ) << '\n' // know or knows
             << replace_word( str, "know(\\w*)" ) << '\n' ; // know followed by zero or more alphanumeric characters
}

I know. You know I know. I know you know I know. We know Henry knows, and Henry knows we know. We're a knowledgeable family.
I . You I . I you I . We Henry knows, and Henry knows we . We're a knowledgeable family.
I . You I . I you I . We Henry , and Henry we . We're a knowledgeable family.
I . You I . I you I . We Henry , and Henry we . We're a family.

http://coliru.stacked-crooked.com/a/ded671ce7efc0a4e

[kalki]

Say,
string str="Hello world";
string str1="wo";

I want to remove white space and other string except "wo" from "Hello world".

[coder777]

if(str.find(str1) != std::string::npos)
  str = str1;

?

[kalki]

Finally i got it >>

#include <iostream>
#include <string>
using namespace std;
int main ()
{
std::string myStr = "http://www.cplusplus.com/forum/ost.cgi.1" ;
std::string s ="ost.cgi";
std::string::size_type len = myStr.find(s);
if(len != std::string::npos)
{
      std::string str = myStr.erase(0, len).erase(s.length());
cout<<str<<endl;
}

else
{
cout<<"not matching"<<endl;
}
return 0;
}

[coder777]

It is actually the same.

std::string str = myStr.erase(0, len).erase(s.length()); = str = s;

or do you see a difference?

[kalki]

@coder777: Yeah both are same. I agree with you. Thank you for your reply.