istringstream "hexadecimal string" value

[ma740988]

The string object value_f doesn't produce the right output. At issue,
- I suspect - is the conversion from string to int with istringstream.
An alternate approach? Thanks in advance

#include <iostream>
#include <sstream>
#include <string>

using namespace std;

// Conversion Functions
template<typename T>
T fromString(const std::string& s) {
std::istringstream is(s);
T t;
is >> t;
return t;
}
template<typename T>
std::string toString(const T& t) {
std:stringstream s;
s << t;
return s.str();
}


//
// test function to convert values:
// 0xAFFF from string to int
// 0xAFFF from int to string

int main()
{

int d(0xAFFF);
string value_d = toString( d );
cout << "value_d is [" << value_d << "]" << endl;

string value_e( " 4999 " );
string value_f( " 0xAFFF " );

int val_1 = fromString<int>( value_e );
cout << "val_1 is [" << val_1 << "]" << endl;
int val_2 = fromString<int>( value_f );
cout << "val_2 is [" << val_2 << "]" << std::hex << endl;

}

 

[Victor Bazarov]

The string object value_f doesn't produce the right output. At issue,
- I suspect - is the conversion from string to int with istringstream.
An alternate approach?

The default extraction operator with default format setting expects
a _decimal_ notation.

Thanks in advance

#include <iostream>
#include <sstream>
#include <string>

using namespace std;

// Conversion Functions
template<typename T>
T fromString(const std::string& s) {

Change to

T fromString(const std::string& s,
std::ios_base& (*f)(std::ios_base&) = std::dec) {

std::istringstream is(s);
T t;
is >> t;

Change to

is >> f >> t;

return t;
}
template<typename T>
std::string toString(const T& t) {

Change to

std::string toString(const T& t,
std::ios_base& (*f)(std::ios_base&) = std::dec) {

std:stringstream s;
s << t;

Change to

s << f << t;

return s.str();
}


//
// test function to convert values:
// 0xAFFF from string to int
// 0xAFFF from int to string

int main()
{

int d(0xAFFF);
string value_d = toString( d );
cout << "value_d is [" << value_d << "]" << endl;

string value_e( " 4999 " );
string value_f( " 0xAFFF " );

int val_1 = fromString<int>( value_e );
cout << "val_1 is [" << val_1 << "]" << endl;
int val_2 = fromString<int>( value_f );

Change to

cout << "val_2 is [" << val_2 << "]" << std::hex << endl;

}

HTH

V

 

[ma740988]

int main()
{

int d(0xAFFF);
string value_d = toString( d );
cout << "value_d is [" << value_d << "]" << endl;

string value_e( " 4999 " );
string value_f( " 0xAFFF " );

int val_1 = fromString<int>( value_e );
cout << "val_1 is [" << val_1 << "]" << endl;
int val_2 = fromString<int>( value_f );

Change to

cout << "val_2 is [" << val_2 << "]" << std::hex << endl;

}

HTH

V

Beautiful. One question though (Haven't gotten through Langer/Kreft)
oct doesn't co-operate

template<typename T>
T fromString(const std::string& s,
std::ios_base& (*f)(std::ios_base&) = std::dec)
{
std::istringstream is(s);
T t;
is >> f >> t;
return t;
}

string value_e( " 4999 " );
int val_e = fromString<int>( value_e, oct);
The output is 4.

 

[Victor Bazarov]

[..] One question though (Haven't gotten through Langer/Kreft)
oct doesn't co-operate

template<typename T>
T fromString(const std::string& s,
std::ios_base& (*f)(std::ios_base&) = std::dec)
{
std::istringstream is(s);
T t;
is >> f >> t;
return t;
}

string value_e( " 4999 " );
int val_e = fromString<int>( value_e, oct);
The output is 4.

'9' is not a valid input for the octal converter, is it?

V

 

[ma740988]

[..] One question though (Haven't gotten through Langer/Kreft)
oct doesn't co-operate

template<typename T>
T fromString(const std::string& s,
std::ios_base& (*f)(std::ios_base&) = std::dec)
{
std::istringstream is(s);
T t;
is >> f >> t;
return t;
}

string value_e( " 4999 " );
int val_e = fromString<int>( value_e, oct);
The output is 4.

'9' is not a valid input for the octal converter, is it?

V

Ah!!! Being 'wrapped up in the stream' , I overlooked that, however it
gets interesting. First, I'm assuming that the stream modifier
std:ct is what you're referring to as the octal converter? Now i
need to grab my text for a refresher but I conclude - based on your
reply - that the conversion is predicated upon passing single digit to
the converter. IOW 4 is passed to the converter, then 9 and so on.

Now, heres a case where the 'octal converter/stream modifier(?)'
produced the desired output which refutes my prior conclusion.

int idx(4999);
cout << oct << idx << endl;

 

[Victor Bazarov]

[..] One question though (Haven't gotten through Langer/Kreft)
oct doesn't co-operate

template<typename T>
T fromString(const std::string& s,
std::ios_base& (*f)(std::ios_base&) = std::dec)
{
std::istringstream is(s);
T t;
is >> f >> t;
return t;
}

string value_e( " 4999 " );
int val_e = fromString<int>( value_e, oct);
The output is 4.

'9' is not a valid input for the octal converter, is it?

V

Ah!!! Being 'wrapped up in the stream' , I overlooked that, however it
gets interesting. First, I'm assuming that the stream modifier
std:ct is what you're referring to as the octal converter? Now i
need to grab my text for a refresher but I conclude - based on your
reply - that the conversion is predicated upon passing single digit to
the converter. IOW 4 is passed to the converter, then 9 and so on.

Now, heres a case where the 'octal converter/stream modifier(?)'
produced the desired output which refutes my prior conclusion.

int idx(4999);
cout << oct << idx << endl;

'oct', like 'dec' or 'hex', control how the string is converted to and
from the internal representation. Those format flags are bi-directional.

You can think of it that they turn on certain converters in the stream.
Once you say 'oct', the next string is interpreted as octal if you input
or the next number is output in the octal form if you output. Converters
are bi-directional too.

V

 

[ma740988]

I'm using google as a newsreader (too cheap right now) and as a result
I dont see your responses momentarily.
In any event, after seeing your use of the fuction pointer that
returns a reference to ios_base. I went back and retrofitted some
'old' code to do the same.
One things that's puzzled me in the past (string related) is the
results of the program below. The output is 0 when i expect 0x00.
0xFF, etc. works fine.


//PARAMETERIZED OVER CHARACTER AND NUMERIC TYPE TO BE CONVERTED
template <typename CT, typename T>
std::basic_string<CT> convertToStr(const T& t, std::ios_base &
(*f)(std::ios_base&), const std::streamsize precision)
{
std::basic_ostringstream<CT> oss;
oss.setf(std::ios::showbase);
oss << std::fixed << std::setprecision(precision)<< f << t;
return oss.str();
};

int main()
{
cout << convertToStr<char>(0x00, std::hex, 0) << endl;
}

 

[Victor Bazarov]

I'm using google as a newsreader (too cheap right now) and as a result
I dont see your responses momentarily.
In any event, after seeing your use of the fuction pointer that
returns a reference to ios_base. I went back and retrofitted some
'old' code to do the same.
One things that's puzzled me in the past (string related) is the
results of the program below. The output is 0 when i expect 0x00.
0xFF, etc. works fine.

I am not surprised. The conversion to hex is done precisely as if it
were done by 'printf'. Since 'printf' never prepends 0 with 0x, neither
does the ostream. The C Standard says that only a non-zero value will
be prefixed with 0x. If you want _all_ values to be prefixed, you should
(a) drop the 'showbase' and (b) add "0x" for the hex.

//PARAMETERIZED OVER CHARACTER AND NUMERIC TYPE TO BE CONVERTED
template <typename CT, typename T>
std::basic_string<CT> convertToStr(const T& t, std::ios_base &
(*f)(std::ios_base&), const std::streamsize precision)
{
std::basic_ostringstream<CT> oss;
oss.setf(std::ios::showbase);
oss << std::fixed << std::setprecision(precision)<< f << t;
return oss.str();
};

int main()
{
cout << convertToStr<char>(0x00, std::hex, 0) << endl;
}

V