【c++基础】C++编写Config类读取配置文件

前言

系统程序一般需要读取参数文件，看到一个很好的Config类记录在此。

头文件Config.h

//Config.h  
//re: https://blog.csdn.net/David_xtd/article/details/9320549
#pragma once  
  
#include <string>  
#include <map>  
#include <iostream>  
#include <fstream>  
#include <sstream>  
  
  
/* 
* rief 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;  
    Trim(key);  
    Trim(v);  
    m_Contents[key] = v;  
    return;  
}  

源文件Config.cpp

// Config.cpp  
  
#include "Config.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[] = " 
	v
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 += "
";  
                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);  
}  

主程序测试文件main.cpp

//main.cpp  
#include "Config.h"  
int main()  
{  
    int port;  
    std::string ipAddress;  
    std::string username;  
    std::string password;  
    const char ConfigFile[]= "..//src//config.txt";   
    Config configSettings(ConfigFile);  
      
    port = configSettings.Read("port", 0);  
    ipAddress = configSettings.Read("ipAddress", ipAddress);  
    username = configSettings.Read("username", username);  
    password = configSettings.Read("password", password);  
    std::cout<<"port:"<<port<<std::endl;  
    std::cout<<"ipAddress:"<<ipAddress<<std::endl;  
    std::cout<<"username:"<<username<<std::endl;  
    std::cout<<"password:"<<password<<std::endl;  
    //
    float level = configSettings.Read("level", level);  
    std::cout<<"level:"<<level<<std::endl;  
  
    return 0;  
}  

参数配置文件实例config.txt

ipAddress=10.10.90.125 
port = 3001; 
username=mark 
password=2d2df5a
level = 0.11 

疑问

1. 头文件中Config类定义之后的函数为什么要写在文件内类外呢？可以写到源文件中吗？

参考

1. 使用Config类读取配置文件；

完