How to adapt to read a file in different formats?
Hello,
I am in a mess I wouldn't know what to do if I were to retrieve data from a file in different formats. For example :
(1)
Wales 0.12 60
Ronaldo 0.25 140 |
(2)
Wales,0.12,60
Ronaldo,0.25,140 |
(3)
Wales , 0.12 , 60
Ronaldo , 0.25 , 140 |
(4)
Wales
0.12
60
// This newline character here is on purpose
Ronaldo
0.25
140 |
Could anyone give me the best approach for each situation I have mentioned? I am new to std::ifstream and any help would be very appreciated.
Thanks in advance.
If the first field (name) does not contain embedded commas or white spaces,
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|
#include <iostream>
#include <cctype>
#include <locale>
#include <vector>
#include <string>
#include <fstream>
#include <iomanip>
namespace utility
{
// This ctype facet classifies comma as whitespace
// http://en.cppreference.com/w/cpp/locale/ctype_char
struct comma_is_ws : std::ctype<char>
{
// http://en.cppreference.com/w/cpp/locale/ctype_char/table
static const mask* classification_table()
{
// start with the classic table ( C locale's table )
static std::vector<mask> table( classic_table(), classic_table() + table_size ) ;
static constexpr char comma = ',' ;
table[comma] = space ; // comma is to be treated as whitespace
return std::addressof( table.front() ) ;
}
// do not delete table, initial reference count == 0
comma_is_ws() : std::ctype<char>( classification_table() ) {}
};
}
int main()
{
const std::string test_file_name = "assorted_formats.txt " ;
{
// create a test file
std::ofstream(test_file_name) <<
"Wales 0.12 60\n"
"Ronaldo 0.25 140\n"
"\n"
"Wales,0.12,60\n"
"Ronaldo,0.25,140\n"
"\n"
"Wales , 0.12 , 60\n"
"Ronaldo , 0.25 , 140\n"
"\n"
"\n"
"Wales\n"
"0.12\n"
"60\n"
"\n" // This newline character here is on purpose
"Ronaldo\n"
"0.25\n"
"140\n" ;
}
{
// view the contents of the test file
std::cout << std::ifstream(test_file_name).rdbuf() << "\n\n----------\n\n" ;
}
{
// open the file for reading
std::ifstream file(test_file_name) ;
// configure it to treat comma as whitespace
// http://en.cppreference.com/w/cpp/io/basic_ios/imbue
file.imbue( std::locale( file.getloc(), new utility::comma_is_ws() ) ) ;
std::string name ;
double number1 ;
int number2 ;
int rec_cnt = 0 ;
while( file >> name >> number1 >> number2 )
{
std::cout << '#' << ++rec_cnt << ". " << std::setw(10) << std::quoted(name)
<< " " << number1 << " " << std::setw(3) << number2 << '\n' ;
}
}
}
|
If you are new to standard streams and locales, this would look intimidating. It is not as esoteric as it appears at first sight.
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