Decode 32-bit string

[kraigballa]

Alright I have a 32-bit string that is nothing but zeros and ones. Each 5 bits represents a different section of the instruction format. Then the last section will have 7 bits (the leading two are fillers).

Here's an example:

im1.store("10111000010000100010000110000000", 1); // Storing 32-bit string into index 1 of Instruction Memory
string binary = im1.fetch(count); // Fetching that string and storing into string variable binary 

So num1 = binary.substr(0, 5) is going to be "10111" in this scenario.

num1[0] = 1;
num1[1] = 0;
num1[2] = 1;
num1[3] = 1;
num1[4] = 1; // Just showing what each bit will be. Still string though 

However, it is still a string. How can go about turning each string bit into an int (there will only be zeros and ones still) that way I can do a binary to decimal conversion? I've tried atoi, and strtol, but nothing seems to be working out. I deleted my previous post, because I don't feel that I asked the question correctly.

[guestgulkan]

calculating an number from a string consisting '1s' and '0s' to an integer is simple enough;

    string binaryStr("0011");//some string or the other
    
    int result =0 ;

    for(size_t count = 0; count < binaryStr.length() ; ++count)
    {
        result *=2;
        result += binaryStr[count]=='1'? 1 :0;
    }

[kraigballa]

Can you explain what lines 7 and 8 are doing? I tested the code and the result was 3. So its changing string to int and binary to decimal...

Also what if you have a 32-bit string? Is there an easy way to split it up into five bits and do what you did?

[simeonz]

You could also use the bitset constructor with strings. See http://www.cplusplus.com/reference/stl/bitset/bitset/

Regards

[krishnendu]

You can certainly use strtol for this purpose. Go through the following code.

#include <string>
#include <cstdlib>
#include <iostream>

using namespace std;

int main (void)
{
	string str = "11001"; // binary representation of 25.
	cout << strtol (str.c_str (), NULL, 2) << endl;
	// The third argument of strtol is the base of the number system.

	return 0;
}

Refer to http://www.cplusplus.com/reference/clibrary/cstdlib/strtol/ for complete documentation on strtol.

[PanGalactic]

bitset has a better interface than strtol() because it will throw if the input is invalid. While you can detect errors with strtol(), it is clumsy to use and commonly ignored.

[kraigballa]

krishnendu, that worked like a charm. A lot less code than what I had. Thanks