Thread: Easy Way To Replace Strings...

Do you want to use ONLY $myvar, or any arbitrary name starting with $?

If the second, then I suggest using a std::map<std::string, std::string> to store key/value pairs. In this case, the key would be "myvar" (or "$myvar") and the value would be the string to replace with.

You probably want to use some kind of string tokenizer to parse your scripts, I recommend downloading Boost and installing it; it's extentions to the standard library (by most of the same people who did the STL). They have a good string tokenizer template class for easy tokenizing. You can iterate through each token of a string, and build the desired output string.

Here is one example:

Code:

#include <iostream>
#include <string>
#include <map>
#include<boost/tokenizer.hpp>


//typedefs to make life easier
typedef std::map<std::string,std::string> stringmap;
typedef boost::char_separator<char> cSeparator;
typedef boost::tokenizer<cSeparator> sTokenizer;
typedef sTokenizer::iterator stIter;

int main()
{
    // Create the variable map:
    stringmap smVariables;
    smVariables["$myVar"] = "<<Contents>>";

    //Create some strings:
    std::string input("This is $notavar   '$myVar':    $myVar");
    std::string output;
    std::string tokens;

    // Setup the separator list:
    cSeparator sep(" \t\n");
    // Create the tokenizer:
    sTokenizer tok(input,sep);
    //Loop through the tokens:
    for(stIter i=tok.begin(); i!=tok.end();++i){
        tokens += "[" + *i + "]";
        if((*i)[0] == '$') // Tokens beginning with '$' get replaced.
            output += "[" + smVariables[*i] + "]";
        else
            output += "[" + *i + "]";
    }

    // Let's see how it works.
    std::cout << "Input  : " << input << std::endl;
    std::cout << "Tokens : " << tokens << std::endl;
    std::cout << "Output : " << output << std::endl;
}

The output of that test case was:

Code:

Input  : This is $notavar   '$myVar':    $myVar
Tokens : [This][is][$notavar]['$myVar':][$myVar]
Output : [This][is][]['$myVar':][<<Contents>>]

This string tokenizer is capable of more powerful things, so it should be able to handle whatever you need.

If you don't want to use the tokenizer, you need to find a way to isolate a substring which contains the variable name, and replace it in a similar fashion.

However, finding "$bob" out of "$bobize" is gonna be somewhat tricky. Can take very long, especially if the user types something insane like "replace$thisMySpaceIsBrokenMySpaceIsBrokenMySpace IsBrokenMySpaceIsBrokenMySpaceIsBrokenMySpaceIsBro kenMySpaceIsBrokenMySpaceIsBrokenMySpaceIsBrokenMy SpaceIsBrokenMySpaceIsBrokenMySpaceIsBrokenMySpace IsBrokenMySpaceIsBrokenMySpaceIsBrokenMySpaceIsBro kenMySpaceIsBrokenMySpaceIsBrokenMySpaceIsBrokenMy SpaceIsBrokenMySpaceIsBrokenMySpaceIsBrokenMySpace IsBrokenMySpaceIsBrokenMySpaceIsBrokenMySpaceIsBro kenMySpaceIsBrokenMySpaceIsBrokenMySpaceIsBrokenMy SpaceIsBrokenMySpaceIsBrokenMySpaceIsBrokenMySpace IsBrokenMySpaceIsBrokenMySpaceIsBrokenMySpaceIsBro kenMySpaceIsBrokenMySpaceIsBrokenMySpaceIsBrokenMy SpaceIsBrokenMySpaceIsBrokenMySpaceIsBrokenMySpace IsBrokenMySpaceIsBrokenMySpaceIsBrokenMySpaceIsBro kenMySpaceIsBrokenMySpaceIsBrokenMySpaceIsBroken".
This means you have to check everything after the $ for being a variable, snipping off one character at a time, and you have to start with the longest possible name (else short variable names override long).

Perl uses this syntax for such cases:
${varname}asdadsadaf

Here's something simple I cooked up. Pretty basic, it simply searches for a pair of matching $ $s, takes what's between them and searches the map for it, and replaces.

Code:

#include <iostream>
#include <string>
#include <map>

typedef std::map<std::string, std::string> stringMap;

std::string parse(std::string s, const stringMap& m){
    std::string::size_type first = 0,second;
    while(true){
        if ((first = s.find("$",first)) == s.npos) break;
        if ((second = s.find("$",first + 1)) == s.npos) break;
        
        std::string key = s.substr(first + 1, second-first-1), val;
        stringMap::const_iterator i = m.find(key);
        if (i != m.end()) val = i->second;
        s.replace(first, second-first + 1, val);

        first = second + 1;
    }
    return s;
}

int main(){
    stringMap m;
    m["cd"] = "[Test string here]";
    std::string s = parse("ab$cd$$$efg$h$i$jkl",m);
    std::cout << s << std::endl;
    
}

This does the following replacements:

$cd$ is replaced by [Test string here]
$$ is replaced by nothing (key doesn't exist)
$h$ is replaced by nothing (key doesn't exist)
Last $ is left alone (it's unmatched)

so the output is:

Code:

ab[Test string here]efgi$jkl

This does present problems if you have any $s in the string that you don't want to be made into a variable name. You could use some kind of escape sequence for the character $, like use $$. You'd have to modify the position searching algorithm slightly; you'd probably want to code your own find() command.