replacing a substring of a string with another string

This is a discussion on replacing a substring of a string with another string within the C++ Programming forums, part of the General Programming Boards category; How can I use string.replace() to do something like: Code: string str, str2, str3; str = "an adequate amount of ...

  1. #1
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    replacing a substring of a string with another string

    How can I use string.replace() to do something like:

    Code:
    string str, str2, str3;
    str  = "an adequate amount of text";
    str2 = "amount of ";
    st3 = "";
    
    str.replace(str2, str3); // an adequate text
    
    //or
    str  = "an adequate amount of text";
    str3 = "[how did this get here?]";
    
    str.replace(str2, str3); // an adequate [how did this get here?] text
    From looking at the documentation, it seems that replace() will not replace more than the amount of text it's replacing.

  2. #2
    Frequently Quite Prolix dwks's Avatar
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    replace() has many forms. http://www.cplusplus.com/reference/s...g/replace.html

    I suspect the first one will suit your needs.
    Code:
    string& replace ( size_t pos1, size_t n1,   const string& str );
    For example, this should print 1cat4.
    Code:
    string original = "1234";
    string replace = "cat";
    // replace original[1] .. original[2] ("23") with "cat"
    original.replace(1, 2, replace);
    cout << original;
    Hopefully I thought that through correctly . . . and hopefully I've answered your question.

    [edit] In your first case, maybe you want something like this.
    Code:
    string str, str2, str3;
    str  = "an adequate amount of text";
    str2 = "amount of ";
    st3 = "";
    
    while(1) {
        // search for an occurance of str2 in str
        size_t found = str.find(str2);
    
        // if such a substr was found,
        if(found != string::npos) {
            // replace it with str3
            str.replace(found, str2.length(), str3);
        }
        else break;  // if the substring wasn't found, exit the loop
    }
    See also http://www.cplusplus.com/reference/s...ring/find.html
    [/edit]
    Last edited by dwks; 10-14-2008 at 05:11 PM.
    dwk

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  3. #3
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    You have to find str2 in str before calling replace. The find function will return an index which can be passed to replace (along with the length of str2) to indicate the location of the substring to be removed.

  4. #4
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    Ah, thank you. I read the example wrong, and it looked like replace(p, n, str) only replaced a maximum on n bytes.

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