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Posted 8 Jul 2013

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6 Nov 2014CPOL2 min read
Designed to take XML and make it easy to read, by adding appropriate line breaks and tab indentation.


This is designed to take XML and make it easy to read, by adding appropriate line breaks and tab indentation.

I wrote this a few nights ago because I got sick of the XML's my work transmits (about 40mb), all on one line (save bandwidth). Notepad++ has a lovely plugin which does this tidy up, but was taking about 45 mins to do a file. This does it in about 5 seconds.

Since I only had the XML's I have to use to test on, there are probably some things I've overlooked. If you find that some XML's are not getting new lined \ indented properly, please send me a sample one.

Using the code 

This little function will take 2 arguments, an input and output stream.  Read through the input stream, format it, and write to the output stream.

I've written a very crude Win32 API input and output selection area, for simple usage. The original version I wrote just involved chucking the EXE in a directory with some XML's, double clicking it, and it would do every XML in that directory.

While the interface is obviously windows only, the actual function itself should be platform independent.

To call this function use

tidyXML(inputFile, outputFile);

With both inputFile and outputFile being references to the ifstream and ofstream.

Here is the function itself. Okay, I'm a bit lazy with comments. If you don't understand why a certain bit is done a certain way, or just want me to comment specific places, let me know in the comments below, and I'll try adding some more. But it should be pretty self explanatory.

void tidyXML(ifstream &input, ofstream &output) {
    char currChar;
    char nextChar;
    int indent = -1;

    string currKeyStore = "";
    string lastKeyStore = "";
    string valueOrJunkStore = "";

    bool inKey = false;
    bool skipNextIndent = false;

    enum keyType {
    keyType lastKeyType = unset, currKeyType = unset;

    while(true) {
        currChar = input.get();
        if (!input.good()) {
            output << currKeyStore;

        // have a gander what's next
        nextChar = input.peek();
        if (!input.good())
            nextChar = '\0';

        if (currChar == '<') {
            inKey = true;

            lastKeyType = currKeyType;
            lastKeyStore = currKeyStore;

            currKeyType = unset;
            currKeyStore = "";

            // if cannot work out here, need to wait until nextChar is '>' to decide
            if (nextChar == '/')
                currKeyType = exitKey;
            else if (nextChar == '?' || nextChar == '!')
                currKeyType = infoLine;

        if (currKeyType == unset && nextChar == '>') {
            // can actually work out what this is now :)
            if (currChar == '/')
                currKeyType = emptyValue;
                currKeyType = entryKey;

        if (inKey)
            currKeyStore += currChar;
            valueOrJunkStore += currChar;

        if (currChar == '>') {
            inKey = false;

            if (!skipNextIndent)
                for (int i = 0; i < indent; ++i)
                    output << '\t';
            output << lastKeyStore;
            skipNextIndent = false;

            if (lastKeyType == entryKey && currKeyType == exitKey) { // value line
                skipNextIndent = true;
                output << valueOrJunkStore;
            } else if (lastKeyType != unset) { // so don't add line at start of the file
                output << endl;

            valueOrJunkStore = "";

            if (lastKeyType == exitKey || lastKeyType == emptyValue)

            if (currKeyType == entryKey || currKeyType == emptyValue)

I compiled the sample version (with a crude Win32 interface) using MinGW. With the following command:

mingw32-g++ --std=c++0x -Wall -fno-builtin -O3 -static *.cpp -lcomdlg32 -o tidyxml.exe

I've static linked it so that it should run as-is, without the dependency hell you can get.

Also provided is the double click build.bat file i use. It'll also strip out the debugging symbols.

Points of Interest

The main pain with writing this, is that you have to always read the next tag, before you know what to do with the current one. Or better put, save the current tag, read the next tag, so you can decide what to do with the saved tag. 

The original version was just full of bools to plan it all out and track everything. These were replaced by the enum which makes the code a lot cleaner and easier to follow. Well I think so anyway.


  • v1 - Original release. 
  • Renamed main function of formatXML to tidyXML . Split demo project out of source file which includes this function.


This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

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Comments and Discussions

QuestionMy experience on MAC OS with homebrewn Parsers isnt so good Pin
KarstenK4-Feb-15 20:58
mveKarstenK4-Feb-15 20:58 
QuestionNice tool (my 5) Pin
H.Brydon6-Aug-13 12:03
professionalH.Brydon6-Aug-13 12:03 
GeneralMy vote of 5 Pin
kanalbrummer15-Jul-13 18:03
kanalbrummer15-Jul-13 18:03 
GeneralMy vote of 5 Pin
Silvabolt10-Jul-13 4:48
Silvabolt10-Jul-13 4:48 
GeneralMy vote of 1 Pin
skyformat99@gmail.com9-Jul-13 20:38
skyformat99@gmail.com9-Jul-13 20:38 
GeneralRe: My vote of 1 Pin
MrMikeJJ9-Jul-13 20:47
MrMikeJJ9-Jul-13 20:47 
GeneralRe: My vote of 1 Pin
kanalbrummer15-Jul-13 18:01
kanalbrummer15-Jul-13 18:01 

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