How to find and replace string?
Do we really need a Boost library for seemingly such a simple task?
To replace all occurences of a substring use this function:
std::string ReplaceString(std::string subject, const std::string& search,
const std::string& replace) {
size_t pos = 0;
while ((pos = subject.find(search, pos)) != std::string::npos) {
subject.replace(pos, search.length(), replace);
pos += replace.length();
}
return subject;
}
If you need performance, here is an optimized function that modifies the input string, it does not create a copy of the string:
void ReplaceStringInPlace(std::string& subject, const std::string& search,
const std::string& replace) {
size_t pos = 0;
while ((pos = subject.find(search, pos)) != std::string::npos) {
subject.replace(pos, search.length(), replace);
pos += replace.length();
}
}
Tests:
std::string input = "abc abc def";
std::cout << "Input string: " << input << std::endl;
std::cout << "ReplaceString() return value: "
<< ReplaceString(input, "bc", "!!") << std::endl;
std::cout << "ReplaceString() input string not modified: "
<< input << std::endl;
ReplaceStringInPlace(input, "bc", "??");
std::cout << "ReplaceStringInPlace() input string modified: "
<< input << std::endl;
Output:
Input string: abc abc def
ReplaceString() return value: a!! a!! def
ReplaceString() input string not modified: abc abc def
ReplaceStringInPlace() input string modified: a?? a?? def
Yes: replace_all
is one of the boost string algorithms:
Although it's not a standard library, it has a few things on the standard library:
- More natural notation based on ranges rather than iterator pairs. This is nice because you can nest string manipulations (e.g.,
replace_all
nested inside atrim
). That's a bit more involved for the standard library functions. - Completeness. This isn't hard to be 'better' at; the standard library is fairly spartan. For example, the boost string algorithms give you explicit control over how string manipulations are performed (i.e., in place or through a copy).
#include <iostream>
#include <string>
using namespace std;
int main ()
{
string str("one three two four");
string str2("three");
str.replace(str.find(str2),str2.length(),"five");
cout << str << endl;
return 0;
}
Output
one five two four
Replace first match
Use a combination of std::string::find
and std::string::replace
.
Find the first match:
std::string s;
std::string toReplace("text to replace");
size_t pos = s.find(toReplace);
Replace the first match:
s.replace(pos, toReplace.length(), "new text");
A simple function for your convenience:
void replace_first(
std::string& s,
std::string const& toReplace,
std::string const& replaceWith
) {
std::size_t pos = s.find(toReplace);
if (pos == std::string::npos) return;
s.replace(pos, toReplace.length(), replaceWith);
}
Usage:
replace_first(s, "text to replace", "new text");
Demo.
Replace all matches
Define this O(n) method using std::string
as a buffer:
void replace_all(
std::string& s,
std::string const& toReplace,
std::string const& replaceWith
) {
std::string buf;
std::size_t pos = 0;
std::size_t prevPos;
// Reserves rough estimate of final size of string.
buf.reserve(s.size());
while (true) {
prevPos = pos;
pos = s.find(toReplace, pos);
if (pos == std::string::npos)
break;
buf.append(s, prevPos, pos - prevPos);
buf += replaceWith;
pos += toReplace.size();
}
buf.append(s, prevPos, s.size() - prevPos);
s.swap(buf);
}
Usage:
replace_all(s, "text to replace", "new text");
Demo.
Boost
Alternatively, use boost::algorithm::replace_all
:
#include <boost/algorithm/string.hpp>
using boost::replace_all;
Usage:
replace_all(s, "text to replace", "new text");