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Sep 18th, 2007

Conversion from char to decimal(int)

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I've read 4 consecutive bytes from a binary file, and store the value as follows,

C++ Syntax (Toggle Plain Text)
int main()
{
char next4[4] ; 
 
while(!fileopen.eof())
{
        fileopen.read (next4, 4 ) ;
}
 
}
int main()
{
char next4[4] ; 

while(!fileopen.eof())
{
        fileopen.read (next4, 4 ) ;
}

}

What I want to do is, that value in next4 want to convert into a decimal/int value. How can I do that. Search on MSDN and unable to find a clear explanation.

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eranga262154

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Sep 18th, 2007

Re: Conversion from char to decimal(int)

you could have read it directly into the integer

C++ Syntax (Toggle Plain Text)
long next4;
 fileopen.read (&next4, sizeof(long) ) ;
long next4;
 fileopen.read (&next4, sizeof(long) ) ;

or you can use the assignment statement

C++ Syntax (Toggle Plain Text)
int main()
{
char next4[4] ; 
int num;
while(!fileopen.eof())
{
        fileopen.read (next4, 4 ) ;
        num = *(int *)next4;
}
 
}
int main()
{
char next4[4] ; 
int num;
while(!fileopen.eof())
{
        fileopen.read (next4, 4 ) ;
        num = *(int *)next4;
}

}

A third way is to use memcpy() to copy the data

C++ Syntax (Toggle Plain Text)
int num;
...
memcpy(&num, next4, sizeof(long));
int num;
...
memcpy(&num, next4, sizeof(long));

Last edited by Ancient Dragon; Sep 18th, 2007 at 8:35 am.

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Sep 18th, 2007

Re: Conversion from char to decimal(int)

Thanks,

What is the wrong with this code.

C++ Syntax (Toggle Plain Text)
char_traits<char>::char_type ch = next4[4] ;
char_traits<char>::int_type int_val ;
int_val = char_traits<char>::to_int_type (ch) ;
char_traits<char>::char_type ch = next4[4] ;
char_traits<char>::int_type int_val ;
int_val = char_traits<char>::to_int_type (ch) ;

eranga262154

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Sep 18th, 2007

Re: Conversion from char to decimal(int)

>>What is the wrong with this code
Nothing that I know of, other than it doesn't work

This produces the wrong value, probably because line 10 is only one byte of a 4-byte number.

C++ Syntax (Toggle Plain Text)
#include <iostream>
#include <string>
using namespace std ;
 
int main()
{
    char next4[4] = {0};
    int n = 123;
    memcpy(next4, &n, sizeof(int));
    char_traits<char>::char_type ch = next4[4] ;
    char_traits<char>::int_type int_val ;
    int_val = char_traits<char>::to_int_type (ch) ;
 
    cout << "int_val = " << int_val << "\n";
    return 0;
 
}
#include <iostream>
#include <string>
using namespace std ;

int main()
{
    char next4[4] = {0};
    int n = 123;
    memcpy(next4, &n, sizeof(int));
    char_traits<char>::char_type ch = next4[4] ;
    char_traits<char>::int_type int_val ;
    int_val = char_traits<char>::to_int_type (ch) ;

    cout << "int_val = " << int_val << "\n";
    return 0;

}

Last edited by Ancient Dragon; Sep 18th, 2007 at 8:55 am.

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Sep 19th, 2007

Re: Conversion from char to decimal(int)

Click to Expand / Collapse Quote originally posted by Ancient Dragon ...

>>What is the wrong with this code
Nothing that I know of, other than it doesn't work This produces the wrong value, probably because line 10 is only one byte of a 4-byte number.

Thanks, I got the point and stuck with this whole night. When I use it only on byte count there in my code.

Thanks again,

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