Question

I think my understanding of bytes arrays and char arrays is causing me some issues, here is my problem:

I have an application that pulls messages from Websphere MQ and sends them onto a target system.

A MQ message has a MQBYTE24 (byte array 24 essentially) that represents the MSGID of the message. My goal is to convert this to a hexidecimal string.

On the WMQ explorer on my Linux box message 1 in the queue has a message identifier of “AMQ QM01” (at least that it what it looks like), and the bytes are below as displayed in the explorer:

00000   41 4D 51 20 51 4D 30 31--20 20 20 20 20 20 20 20  |AMQ QM01        |
00010   BD F4 A8 4E A2 A3 06 20--                         |...N...         |

Now when my code runs I pick up that same message id and try convert it to a hex string.

The exact message id while debugging is:

AMQ QM01 \275\364\250N\242\243\006

And after running through my conversion (code below) i get:

414D5120514D30312020202020202020FFFFFF4EFFFF6

As you can see it is slightly different to the one that the WMQ Explorer shows, any idea what i am doing wrong here?

I assume it is me converting from the MQBYTE24 to char….something is going wrong there…

Below is a small sample program that produces the “wrong result”…..i assune i must use a byte array instead of char?

The output for the following is:

Result: 414D5120514D30312020202020202020FFFFFF4EFFFF6

#include <stdio.h>
#include <string.h>
#include <stdlib.h>

int main(){   
    char name[41]="AMQ QM01        \275\364\250N\242\243\006";
    char buffer[82]="";
    char *pbuffer = buffer;
    FILE *fp_1;
    FILE *fp_2;
    int size;
    char *buffer_1 = NULL;
    char *buffer_2 = NULL;

    int rc = convertStrToHex(buffer, name);
    printf( "Result: %s\n", pbuffer ); 
    }
    return 0;
}

int convertStrToHex(char *buffer, char str[10]){
    int len = strlen(str);
    int i;

    for( i = 0; i < len ;i++ ){
        sprintf(buffer, "%X", str[i]);
        buffer +=2;
    };
}

Thanks for the help 🙂

Lynton

Answer 1

As several other answers already point out, you need to cast the characters to unsigned char to avoid their being padded with FF to fill a 32-bit int’s worth of bytes. But there’s actually another issue: that lone number 6 at the end will only print as one character in the output. You want each character to take up exactly two positions, so you need a zero-padded field specifier. Putting it all together, you get

sprintf(buffer, "%02X", (unsigned char)str[i]);