C++ character replace

Question

What is the best way to replace characters in a string?

Specifically:

"This,Is A|Test" ----> "This_Is_A_Test"

I want to replace all commas, spaces, and "|" with underscores.

(I have access to Boost.)

Answer 1

The C++ Standard Library has access to these functions as well without using BOOST. Refer to the replace C++ Reference. Is this the best way ? I guess that's up to discussion. To replace multiple / different characters, you may have to call replace more than once.

#include <string>
    string& replace( size_type index, size_type num, const string& str );
    string& replace( size_type index1, size_type num1, const string& str, size_type index2, size_type num2 );
    string& replace( size_type index, size_type num, const Char* str );
    string& replace( size_type index, size_type num1, const Char* str, size_type num2 );
    string& replace( size_type index, size_type num1, size_type num2, Char ch);

    string& replace( iterator start, iterator end, const string& str );
    string& replace( iterator start, iterator end, const Char* str );
    string& replace( iterator start, iterator end, const Char* str, size_type num );
    string& replace( iterator start, iterator end, size_type num, Char ch );
    string& replace( iterator start, iterator end, input_iterator start2, input_iterator end2 );

Example program:

// replacing in a string
#include <iostream>
#include <string>
using namespace std;

int main ()
{
  string base="this is a test string.";
  string str2="n example";
  string str3="sample phrase";
  string str4="useful.";

  // function versions used in the same order as described above:

  // Using positions:                 0123456789*123456789*12345
  string str=base;                // "this is a test string."
  str.replace(9,5,str2);          // "this is an example string."
  str.replace(19,6,str3,7,6);     // "this is an example phrase."
  str.replace(8,10,"just all",6); // "this is just a phrase."
  str.replace(8,6,"a short");     // "this is a short phrase."
  str.replace(22,1,3,'!');        // "this is a short phrase!!!"

  // Using iterators:                      0123456789*123456789*
  string::iterator it = str.begin();   //  ^
  str.replace(it,str.end()-3,str3);    // "sample phrase!!!"
  str.replace(it,it+6,"replace it",7); // "replace phrase!!!"
  it+=8;                               //          ^
  str.replace(it,it+6,"is cool");      // "replace is cool!!!"
  str.replace(it+4,str.end()-4,4,'o'); // "replace is cooool!!!"
  it+=3;                               //             ^
  str.replace(it,str.end(),str4.begin(),str4.end());
                                       // "replace is useful."
  cout << str << endl;
  return 0;
}

Answer 2

EDIT: As Space_C0wb0y said, replace_if is definitely better. Here's some simpler sample code:

#include <string>
#include <iostream>
#include <algorithm>
using namespace std;

bool isBad(char c)
{
 const string bad_chars = "|, ";
 return (bad_chars.find(c) != string::npos);
}

int main()
{
 string str = "This,Is A|Test";

 // Replace!
 replace_if(str.begin(),str.end(),isBad,'_');

 cout<<str<<endl; 
 return 0;
}

OLD ANSWER:

Use std::replace with std::find_first_of

Answer 3

You could use the STL-Algorithm replace_if.

Answer 4

boost::replace_all(s, old, new);

Answer 5

As the other answers indicated, you can use the various replace methods. However, these approaches have the downside of scanning the string multiple times (one time for each character). I would recommend rolling your own replace method, if you care about speed:

void beautify(std::string &s) {
    int i;
    for (i = 0; i < s.length(); ++i) {
        switch (s[i]) {
        case ' ':
        case ',':
        case '|':
            s[i] = '_';
        }
    }
}

Answer 6

I was writing this, when Space_C0wb0y posted his answer, which is the right answer for your question. This is a bit more complicated, but handles more possible replacements.

(sorry, not compiled/tested)

class MyReplacer
{
  friend std::ostream& operator<<(std::ostream& os, const MyReplacer& Repl);
  public:
    MyReplacer(char c) : ch(c) {}
  private:
    char ch;
};

std::ostream& operator<<(std::ostream& os, const MyReplacer& Repl)
{
  switch (Repl.ch)
  {
    case '|':
    case ' ':
    case ',': os << '_'; break;
    default: os << Repl.ch;
  }
  return os;
}


std::ostringstream oss;
std::copy(str.begin(), str.end(), std::ostream_iterator<MyReplacer>(oss));
std::string result = oss.str();

Answer 7

You could use the standard replace_if algorithm, except the predicate is rather complicated (to be expressed inline with current C++ standard and no lambda).

You could write your own, or use is_any_of from boost's string algorithms, so:

#include <algorithm>
#include <string>
#include <boost/algorithm/string/classification.hpp>
#include <iostream>

int main()
{
    std::string s("This,Is A|Test");
    std::replace_if(s.begin(), s.end(), boost::is_any_of(", |"), '_');
    std::cout << s << '\n';
}