c++ template issue [closed] - c++

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Closed 10 years ago.
I'm currently using the class given in this tutorial: http://www.dreamincode.net/forums/topic/183191-create-a-simple-configuration-file-parser/
Initially it worked fine, but since I split the single source file into seperate header and cpp files I've been unable to call the getValueOfKey function
header:
#ifndef CONFIGFILE_H
#define CONFIGFILE_H
#include <iostream>
#include <string>
#include <sstream>
#include <map>
#include <fstream>
#include <typeinfo>
class ConfigFile
{
private:
std::map<std::string, std::string> contents;
std::string fName;
void removeComment(std::string &line) const;
bool onlyWhitespace(const std::string &line) const;
bool validLine(const std::string &line) const;
void extractKey(std::string &key, size_t const &sepPos, const std::string &line) const;
void extractValue(std::string &value, size_t const &sepPos, const std::string &line) const;
void extractContents(const std::string &line);
void parseLine(const std::string &line, size_t const lineNo);
void ExtractKeys();
public:
ConfigFile(const std::string &fName);
bool keyExists(const std::string &key) const;
template <typename ValueType>
ValueType getValueOfKey(const std::string &key, ValueType const &defaultValue) const;
};
#endif /* CONFIGFILE_H */
cpp:
#include "ConfigFile.h"
std::map<std::string, std::string> contents;
std::string fName;
template <typename T>
static std::string T_to_string(T const &val)
{
std::ostringstream ostr;
ostr << val;
return ostr.str();
}
template <typename T>
static T string_to_T(std::string const &val)
{
std::istringstream istr(val);
T returnVal;
if (!(istr >> returnVal))
std::cout << "CFG: Not a valid " << (std::string)typeid (T).name() << " received!\n" << std::endl;
return returnVal;
}
template <>
std::string string_to_T(std::string const &val)
{
return val;
}
void ConfigFile::removeComment(std::string &line) const
{
if (line.find(';') != line.npos)
line.erase(line.find(';'));
}
bool ConfigFile::onlyWhitespace(const std::string &line) const
{
return (line.find_first_not_of(' ') == line.npos);
}
bool ConfigFile::validLine(const std::string &line) const
{
std::string temp = line;
temp.erase(0, temp.find_first_not_of("\t "));
if (temp[0] == '=')
return false;
for (size_t i = temp.find('=') + 1; i < temp.length(); i++)
if (temp[i] != ' ')
return true;
return false;
}
void ConfigFile::extractKey(std::string &key, size_t const &sepPos, const std::string &line) const
{
key = line.substr(0, sepPos);
if (key.find('\t') != line.npos || key.find(' ') != line.npos)
key.erase(key.find_first_of("\t "));
}
void ConfigFile::extractValue(std::string &value, size_t const &sepPos, const std::string &line) const
{
value = line.substr(sepPos + 1);
value.erase(0, value.find_first_not_of("\t "));
value.erase(value.find_last_not_of("\t ") + 1);
}
void ConfigFile::extractContents(const std::string &line)
{
std::string temp = line;
temp.erase(0, temp.find_first_not_of("\t "));
size_t sepPos = temp.find('=');
std::string key, value;
extractKey(key, sepPos, temp);
extractValue(value, sepPos, temp);
if (!keyExists(key))
contents.insert(std::pair<std::string, std::string > (key, value));
else
std::cout << "CFG: Can only have unique key names!\n" << std::endl;
}
void ConfigFile::parseLine(const std::string &line, size_t const lineNo)
{
if (line.find('=') == line.npos)
std::cout << "CFG: Couldn't find separator on line: " << T_to_string(lineNo) << "\n" << std::endl;
if (!validLine(line))
std::cout << "CFG: Bad format for line: " << T_to_string(lineNo) << "\n" << std::endl;
extractContents(line);
}
void ConfigFile::ExtractKeys()
{
std::ifstream file;
file.open(fName.c_str());
if (!file)
std::cout << "CFG: File " << fName << " couldn't be found!\n" << std::endl;
std::string line;
size_t lineNo = 0;
while (std::getline(file, line))
{
lineNo++;
std::string temp = line;
if (temp.empty())
continue;
removeComment(temp);
if (onlyWhitespace(temp))
continue;
parseLine(temp, lineNo);
}
file.close();
}
ConfigFile::ConfigFile(const std::string &fName)
{
this->fName = fName;
ExtractKeys();
}
bool ConfigFile::keyExists(const std::string &key) const
{
return contents.find(key) != contents.end();
}
template <typename ValueType>
ValueType ConfigFile::getValueOfKey(const std::string &key, ValueType const &defaultValue = ValueType()) const
{
if (!keyExists(key))
return defaultValue;
return string_to_T<ValueType> (contents.find(key)->second);
}
I am attempting to call it using the same method as when it was a single file, something like std::cout << Config.getValueOfKey<std::string>("test");, but now I am getting the following compiler error
main.cpp: In function 'int main(int, char**)':
main.cpp:29:71: error: no matching function for call to 'ConfigFile::getValueOfKey(const char [5])'
main.cpp:29:71: note: candidate is:
In file included from main.h:17:0,
from main.cpp:9:
ConfigFile.h:35:12: note: template<class ValueType> ValueType ConfigFile::getValueOfKey(const string&, const ValueType&) const
ConfigFile.h:35:12: note: template argument deduction/substitution failed:
main.cpp:29:71: note: candidate expects 2 arguments, 1 provided
Given my poor grasp on templates I can't really see what this error is trying to tell me, I have tried passing a direct string instead of a char array to no avail. Any help or explanation would be greatly appreciated, my heads worn a nice hole in the desk over the past few hours.

Answer 1

You declared the method taking 2 arguments:
ValueType getValueOfKey(const std::string &key, ValueType const &defaultValue) const;
// | |
// first parameter second parameter
and only supply one:
Config.getValueOfKey<std::string>("test");
I've yet to encounter a compiler that guesses what you mean without any help.
You'll need to move the default to the header file, where you declare the method:
ValueType getValueOfKey(const std::string &key, ValueType const &defaultValue = ValueType()) const;
// | |
// first parameter second parameter
You'll probably get a linker error afterwards, so you might want to check this.