C++编写Config类读取配置文件

摘要: 此篇博文主要是转载自http://blog.csdn.net/huixingshao/article/details/45969887，感谢博主的分享，现只是将代码备份一下至本人博客中而已

// ConfigFile.h

#include <string>
#include <map>
#include <iostream>
#include <fstream>
#include <sstream>

/*
* \brief Generic configuration Class
*
*/
class Config {
// Data
protected:
std::string m_Delimiter;  //!< separator between key and value
std::string m_Comment;    //!< separator between value and comments
std::map<std::string,std::string> m_Contents;  //!< extracted keys and values

typedef std::map<std::string,std::string>::iterator mapi;
typedef std::map<std::string,std::string>::const_iterator mapci;
// Methods
public:

Config( std::string filename,std::string delimiter = "=",std::string comment = "#" );
Config();
template<class T> T Read( const std::string& in_key ) const;  //!<Search for key and read value or optional default value, call as read<T>
template<class T> T Read( const std::string& in_key, const T& in_value ) const;
template<class T> bool ReadInto( T& out_var, const std::string& in_key ) const;
template<class T>
bool ReadInto( T& out_var, const std::string& in_key, const T& in_value ) const;
bool FileExist(std::string filename);
void ReadFile(std::string filename,std::string delimiter = "=",std::string comment = "#" );

// Check whether key exists in configuration
bool KeyExists( const std::string& in_key ) const;

// Modify keys and values
template<class T> void Add( const std::string& in_key, const T& in_value );
void Remove( const std::string& in_key );

// Check or change configuration syntax
std::string GetDelimiter() const { return m_Delimiter; }
std::string GetComment() const { return m_Comment; }
std::string SetDelimiter( const std::string& in_s )
{ std::string old = m_Delimiter;  m_Delimiter = in_s;  return old; }
std::string SetComment( const std::string& in_s )
{ std::string old = m_Comment;  m_Comment =  in_s;  return old; }

// Write or read configuration
friend std::ostream& operator<<( std::ostream& os, const Config& cf );
friend std::istream& operator>>( std::istream& is, Config& cf );

protected:
template<class T> static std::string T_as_string( const T& t );
template<class T> static T string_as_T( const std::string& s );
static void Trim( std::string& inout_s );

// Exception types
public:
struct File_not_found {
std::string filename;
File_not_found( const std::string& filename_ = std::string() )
: filename(filename_) {} };
struct Key_not_found {  // thrown only by T read(key) variant of read()
std::string key;
Key_not_found( const std::string& key_ = std::string() )
: key(key_) {} };
};

/* static */
template<class T>
std::string Config::T_as_string( const T& t )
{
// Convert from a T to a string
// Type T must support << operator
std::ostringstream ost;
ost << t;
return ost.str();
}

/* static */
template<class T>
T Config::string_as_T( const std::string& s )
{
// Convert from a string to a T
// Type T must support >> operator
T t;
std::istringstream ist(s);
ist >> t;
return t;
}

/* static */
template<>
inline std::string Config::string_as_T<std::string>( const std::string& s )
{
// Convert from a string to a string
// In other words, do nothing
return s;
}

/* static */
template<>
inline bool Config::string_as_T<bool>( const std::string& s )
{
// Convert from a string to a bool
// Interpret "false", "F", "no", "n", "0" as false
// Interpret "true", "T", "yes", "y", "1", "-1", or anything else as true
bool b = true;
std::string sup = s;
for( std::string::iterator p = sup.begin(); p != sup.end(); ++p )
*p = toupper(*p);  // make string all caps
if( sup==std::string("FALSE") || sup==std::string("F") ||
sup==std::string("NO") || sup==std::string("N") ||
sup==std::string("0") || sup==std::string("NONE") )
b = false;
return b;
}

template<class T>
T Config::Read( const std::string& key ) const
{
// Read the value corresponding to key
mapci p = m_Contents.find(key);
if( p == m_Contents.end() ) throw Key_not_found(key);
return string_as_T<T>( p->second );
}

template<class T>
T Config::Read( const std::string& key, const T& value ) const
{
// Return the value corresponding to key or given default value
// if key is not found
mapci p = m_Contents.find(key);
if( p == m_Contents.end() ) return value;
return string_as_T<T>( p->second );
}

template<class T>
bool Config::ReadInto( T& var, const std::string& key ) const
{
// Get the value corresponding to key and store in var
// Return true if key is found
// Otherwise leave var untouched
mapci p = m_Contents.find(key);
bool found = ( p != m_Contents.end() );
if( found ) var = string_as_T<T>( p->second );
return found;
}

template<class T>
bool Config::ReadInto( T& var, const std::string& key, const T& value ) const
{
// Get the value corresponding to key and store in var
// Return true if key is found
// Otherwise set var to given default
mapci p = m_Contents.find(key);
bool found = ( p != m_Contents.end() );
if( found )
var = string_as_T<T>( p->second );
else
var = value;
return found;
}

template<class T>
void Config::Add( const std::string& in_key, const T& value )
{
// Add a key with given value
std::string v = T_as_string( value );
std::string key=in_key;
Config::Trim(key);
Config::Trim(v);
m_Contents[key] = v;
return;
}

// ConfigFile.cpp

#include "ConfigFile.h"

using namespace std;

Config::Config( string filename, string delimiter, string comment )
: m_Delimiter(delimiter), m_Comment(comment)
{
// Construct a Config, getting keys and values from given file

std::ifstream in( filename.c_str() );

if( !in ) throw File_not_found( filename );

in >> (*this);
}

Config::Config()
: m_Delimiter( string(1,'=') ), m_Comment( string(1,'#') )
{
// Construct a Config without a file; empty
}

bool Config::KeyExists( const string& key ) const
{
// Indicate whether key is found
mapci p = m_Contents.find( key );
return ( p != m_Contents.end() );
}

/* static */
void Config::Trim( string& inout_s )
{
// Remove leading and trailing whitespace
static const char whitespace[] = " \n\t\v\r\f";
inout_s.erase( 0, inout_s.find_first_not_of(whitespace) );
inout_s.erase( inout_s.find_last_not_of(whitespace) + 1U );
}

std::ostream& operator<<( std::ostream& os, const Config& cf )
{
// Save a Config to os
for( Config::mapci p = cf.m_Contents.begin();
p != cf.m_Contents.end();
++p )
{
os << p->first << " " << cf.m_Delimiter << " ";
os << p->second << std::endl;
}
return os;
}

void Config::Remove( const string& key )
{
// Remove key and its value
m_Contents.erase( m_Contents.find( key ) );
return;
}

std::istream& operator>>( std::istream& is, Config& cf )
{
// Load a Config from is
// Read in keys and values, keeping internal whitespace
typedef string::size_type pos;
const string& delim  = cf.m_Delimiter;  // separator
const string& comm   = cf.m_Comment;    // comment
const pos skip = delim.length();        // length of separator

string nextline = "";  // might need to read ahead to see where value ends

while( is || nextline.length() > 0 )
{
// Read an entire line at a time
string line;
if( nextline.length() > 0 )
{
line = nextline;  // we read ahead; use it now
nextline = "";
}
else
{
std::getline( is, line );
}

// Ignore comments
line = line.substr( 0, line.find(comm) );

// Parse the line if it contains a delimiter
pos delimPos = line.find( delim );
if( delimPos < string::npos )
{
// Extract the key
string key = line.substr( 0, delimPos );
line.replace( 0, delimPos+skip, "" );

// See if value continues on the next line
// Stop at blank line, next line with a key, end of stream,
// or end of file sentry
bool terminate = false;
while( !terminate && is )
{
std::getline( is, nextline );
terminate = true;

string nlcopy = nextline;
Config::Trim(nlcopy);
if( nlcopy == "" ) continue;

nextline = nextline.substr( 0, nextline.find(comm) );
if( nextline.find(delim) != string::npos )
continue;

nlcopy = nextline;
Config::Trim(nlcopy);
if( nlcopy != "" ) line += "\n";
line += nextline;
terminate = false;
}

// Store key and value
Config::Trim(key);
Config::Trim(line);
cf.m_Contents[key] = line;  // overwrites if key is repeated
}
}

return is;
}
bool Config::FileExist(std::string filename)
{
bool exist= false;
std::ifstream in( filename.c_str() );
if( in )
exist = true;
return exist;
}

void Config::ReadFile( string filename, string delimiter,
string comment )
{
m_Delimiter = delimiter;
m_Comment = comment;
std::ifstream in( filename.c_str() );

if( !in ) throw File_not_found( filename );

in >> (*this);
}