How to pass const string parameter from perl to c++ using swig - c++

Question

I am new to Swig and I need help in debugging this error.
My motive is to create a logging system with less time consuming using Swig, C++ , Perl. But i got error while passing the string parameter form Perl to C++ via swig.
I have placed my entire code and error below.
Please help me to solve this issue. Thanks in future.
Logger.cpp
#include <stdexcept>
#include <string>
#include <ctime>
#include "Logger.h"
using namespace std;
Logger* Logger::pInstance = nullptr;
Logger& Logger::instance()
{
lock_guard<mutex> guard(sMutex);
printf("instance");
if (pInstance == nullptr)
pInstance = new Logger();
return *pInstance;
}
void Logger::Cleanup()
{
lock_guard<mutex> guard(Logger::sMutex);
delete Logger::pInstance;
Logger::pInstance = nullptr;
}
Logger::Logger()
{
printf("Constructor\n");
mOutputStream.open("log.out", ios_base::app);
if (!mOutputStream.good()) {
throw runtime_error("Unable to initialize the Logger!");
}
}
void Logger::log(const string& inMessage, const string& inLogLevel)
{
lock_guard<mutex> guard(sMutex);
logHelper(inMessage, inLogLevel);
}
void Logger::logHelper(const std::string& inMessage, const std::string& inLogLevel)
{
mOutputStream << "[ " << current_time() << " ]" << inLogLevel << ": " << inMessage << endl;
}
string Logger::current_time()
{
time_t rawtime;
struct tm * timeinfo;
char buffer[80];
time (&rawtime);
timeinfo = localtime(&rawtime);
strftime(buffer,sizeof(buffer),"%d-%m-%Y %H:%M:%S",timeinfo);
std::string str(buffer);
return str;
}
Logger::~Logger(){
printf("deconstructor\n");
mOutputStream.close();
}
Logger.h
#ifndef LOGGER_H_
#define LOGGER_H_
#include <stdio.h>
#include <iostream>
#include <fstream>
#include <vector>
#include <string>
#include <mutex>
class Logger
{
public:
Logger();
~Logger();
Logger& instance();
void log(const std::string& inMessage,
const std::string& inLogLevel);
protected:
static Logger* pInstance;
std::ofstream mOutputStream;
void Cleanup();
void logHelper(const std::string& inMessage,
const std::string& inLogLevel);
std::string current_time();
private:
std::mutex sMutex;
};
#endif
Logger.i
%module Logger
%{
#include "Logger.h"
%}
%include "Logger.h"
ch.pl
use strict;
use warnings;
use Cwd qw( abs_path );
use File::Basename qw( dirname );
use lib dirname(abs_path($0));
use Logger;
my $p=new Logger::Logger();
$p->instance();
$p->log("test message");
Error message*
TypeError in method 'Logger_log', argument 2 of type 'std::string' at ch1.perl line 19.

Answer 1

You need to include a typemap for std::string in your interface file so SWIG knows how to handle the type, see chapter 9.4 in the manual:
9.4.1 std::string The std_string.i library provides typemaps for converting C++ std::string objects to and from strings in the target
scripting language.
%module Logger
%include "std_string.i"
%{
#include "Logger.h"
%}
%include "Logger.h"
If I use this and run ch.pl like this:
use strict;
use warnings;
use lib '.';
use Logger;
my $p = Logger::Logger->new();
$p->instance();
$p->log("test message", "DEBUG");
I get output:
Constructor
instanceConstructor
deconstructor
The content of the log.out file is:
[ 22-05-2020 17:35:12 ]DEBUG: test message