C++ How-To: Print a Buffer

August 1st, 2009

I was recently writing a command line application in C++ that parses raw binary. I thought it would be really nice to be able to print different parts of memory to the screen as the program runs. I’ve included well-commented code and a usage example.

//needed for printf()
#include <stdio.h>
  
//needed for strlen()
#include <string.h>
  
// prints the contents of memory in hex and ascii.
// starts at the location of the pointer "start"
// prints "length" bytes of memory.
void Print_Memory(const unsigned char * start, unsigned int length)
{
    //create row, col, and i.  Set i to 0
    int row, col, i = 0;
  
    //iterate through the rows, which will be 16 bytes of memory wide
    for(row = 0; (i + 1) < length; row++)
    {
        //print hex representation
        for(col = 0; col<16; col++)
        {
            //calculate the current index
            i = row*16+col;
            
            //divides a row of 16 into two columns of 8
            if(col==8)
                printf(" ");
            
            //print the hex value if the current index is in range.
            if(i<length)
                printf("%02X", start[i]);
            //print a blank if the current index is past the end
            else
                printf("  ");
            
            //print a space to keep the values separate
            printf(" ");
        }
        
        //create a vertial seperator between hex and ascii representations
        printf(" ");
  
        //print ascii representation
        for(col = 0; col<16; col++)
        {
            //calculate the current index
            i = row*16+col;
            
            //divides a row of 16 into two coumns of 8
            if(col==8)
                printf("  ");
            
            //print the value if it is in range
            if(i<length)
            {
                //print the ascii value if applicable
                if(start[i]>0x20 && start[i]<0x7F)  //A-Z
                    printf("%c", start[i]);
                //print a period if the value is not printable
                else
                    printf(".");
            }
            //nothing else to print, so break out of this for loop
            else
                break;
        }
        
        //create a new row
        printf("\n");
    }
}
  
// Prints the contents of memory in hex and ascii.
// Prints the memory between and including the
// two "end1" and "end2" pointers.
void Print_Memory(const unsigned char * end1, const unsigned char * end2)
{
    if(end2 >= end1)
        Print_Memory(end1, end2 - end1 + 1);
    else
        Print_Memory(end2, end1 - end2 + 1);
}
  
int main(int argc, char **args)
{
    const char start [] = "hi there!  You're looking at me in memory!";
    const char * end = start + (int)strlen(start);
  
    Print_Memory((unsigned char *)start, (unsigned char *)end);
  
    return 0;
}

I’ve compiled this code with both g++ and Visual C++.

download here

Here is the program’s output:

68 69 20 74 68 65 72 65  21 20 20 59 6F 75 27 72  hi.there  !..You'r
65 20 6C 6F 6F 6B 69 6E  67 20 61 74 20 6D 65 20  e.lookin  g.at.me.
69 6E 20 6D 65 6D 6F 72  79 21 00                 in.memor  y!.

General, Projects
C#, g++, Programming, Visual C++
1 August 2009 comments [2] TrackBack-URI

2 comments

Marika posted on May 30, 2011:

Thank you! This function saved my day!
Vinai posted on October 6, 2011:

this is very useful and made by debuging easy.