Parsing *.cpp file containing enum using boost::regex.

Question

I alredy parsed file and split content to enum or enum classes.

std::string sourceString = readFromFile(typesHDestination);
boost::smatch xResults;
std::string::const_iterator Start = sourceString.cbegin();
std::string::const_iterator End = sourceString.cend();

while (boost::regex_search(Start, End, xResults, boost::regex("(?<data_type>enum|enum\\s+class)\\s+(?<enum_name>\\w+)\\s*\{(?<content>[^\}]+?)\\s*\}\\s*")))
{
    std::cout << xResults["data_type"]
        << " " << xResults["enum_name"] << "\n{\n";

    std::string::const_iterator ContentStart = xResults["content"].begin();
    std::string::const_iterator ContentEnd = xResults["content"].end();
    boost::smatch xResultsInner;

    while (boost::regex_search(ContentStart, ContentEnd, xResultsInner, boost::regex("(?<name>\\w+)(?:(?:\\s*=\\s*(?<value>[^\,\\s]+)(?:(?:,)|(?:\\s*)))|(?:(?:\\s*)|(?:,)))")))
    {
        std::cout << xResultsInner["name"] << ": " << xResultsInner["value"] << std::endl;

        ContentStart = xResultsInner[0].second;
    }

    Start = xResults[0].second;
    std::cout << "}\n";
}

Its ok if enums are without comments.

I tried to add named group <comment> to save comments in enums, but failed every time. (\/{2}\s*.+) - sample for comments with double slashes.

I tested using this online regex and with boost::regex.

1. The first step - from *.cpp file to <data_type> <enum_name> <content> regex:

(?'data_type'enum|enum\s+class)\s+(?'enum_name'\w+)\s*{\s*(?'content'[^}]+?)\s*}\s*

2. From <content> to <name> <value> <comment> regex:

(?'name'\w+)(?:(?:\s*=\s*(?'value'[^\,\s/]+)(?:(?:,)|(?:\s*)))|(?:(?:\s*)|(?:,)))

The last one contains error. Is there any way to fix it and add feature to store coments in group?

Answer 1

As some comments said, may it is not a good idea to parse a source file with Regular Expression except with some simple cases

for example this source file, from: http://en.cppreference.com/w/cpp/language/enum

#include <iostream>

// enum that takes 16 bits
enum smallenum: int16_t
{
    a,
    b,
    c
};


// color may be red (value 0), yellow (value 1), green (value 20), or blue (value 21)
enum color
{
    red,
    yellow,
    green = 20,
    blue
};

// altitude may be altitude::high or altitude::low
enum class altitude: char
{ 
     high='h',
     low='l', // C++11 allows the extra comma
}; 

// the constant d is 0, the constant e is 1, the constant f is 3
enum
{
    d,
    e,
    f = e + 2
};

//enumeration types (both scoped and unscoped) can have overloaded operators
std::ostream& operator<<(std::ostream& os, color c)
{
    switch(c)
    {
        case red   : os << "red";    break;
        case yellow: os << "yellow"; break;
        case green : os << "green";  break;
        case blue  : os << "blue";   break;
        default    : os.setstate(std::ios_base::failbit);
    }
    return os;
}

std::ostream& operator<<(std::ostream& os, altitude al)
{
    return os << static_cast<char>(al);
}

int main()
{
    color col = red;
    altitude a;
    a = altitude::low;

    std::cout << "col = " << col << '\n'
              << "a = "   << a   << '\n'
              << "f = "   << f   << '\n';
} 

the key pattern here is: starting with enum and end with ; and you cannot predict any text between enum and ; there will be so many possibilities! and for that you can use .*? lazy star

Thus if I want to extract all enums I use:

NOTE: it is not the efficient way

boost::regex rx( "^\\s*(enum.*?;)" );

boost::match_results< std::string::const_iterator > mr; // or boost::smatch


std::ifstream ifs( "file.cpp" );
const uintmax_t file_size = ifs.seekg( 0, std::ios_base::end ).tellg();
                            ifs.seekg( 0, std::ios_base::beg );   // rewind

std::string whole_file( file_size, ' ' );
ifs.read( &*whole_file.begin(), file_size );
ifs.close();

while( boost::regex_search( whole_file, mr, rx ) ){
    std::cout << mr.str( 1 ) << '\n';
    whole_file = mr.suffix().str();
} 

which the output will be:

enum smallenum: int16_t
{
    a,
    b,
    c
};
enum color
{
    red,
    yellow,
    green = 20,
    blue
};
enum class altitude: char
{
     high='h',
     low='l', // C++11 allows the extra comma
};
enum
{
    d,
    e,
    f = e + 2
};

And Of course for such simple thing I prefer to use:

perl -lne '$/=unlef;print $1 while/^\s*(enum.*?;)/smg' file.cpp  

that has the same output.

And may this pattern helps you if you want to match each section separately

^\s*(enum[^{]*)\s*({)\s*([^}]+)\s*(};)

But again this is not a good idea except for some simple source files. Since C++ Source Code has free style and not all code writers follow the standard rules. For example with the pattern above, I assumed that (};) the } comes with ; and if someone separates them ( which is still a valid code ) the pattern will be failed to match.

Answer 2

I argree with the fact that using regex to parse complicated data is not the best solution. I'v made an omission of the few major conditions. First of all, i parsed some kind of generated source code containing emuns and enum classes. So there were no suprises in code, and code was regular. So i parsing regular code with regex.

The Answer: (the first step is the same, the second was fixed) How to parse enums/emun classes with regex:

1. The first step - from *.cpp file to <data_type> <enum_name> <content> regex:

(?'data_type'enum|enum\s+class)\s+(?'enum_name'\w+)\s*{\s*(?'content'[^}]+?)\s*}\s*

2. From <content> to <name> <value> <comment> regex:

^\s*(?'name'\w+)(?:(?:\s*=\s*(?'value'[^,\n/]+))|(?:[^,\s/]))(?:(?:\s$)|(?:\s*,\s*$)|(?:[^/]/{2}\s(?'comment'.*$)))

All test were ok and here is marked text by colors.