Question

My problem is that the strcmp() functions makes the following problems:

main.c:35: warning: passing argument 1 of ‘strcmp’ makes pointer from integer without a cast

While compiling and the following while running the program:

Segmentation fault: 11

I know what the errors means, I just don’t know any other way to do it…Have thought about using itoa() or sprintf(), but i need the checksum in hex so can’t see how I can accomplish that.

The code is as follows:

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

int main()
{
    char nmea[] ="$GPRMC,131637.000,A,5820.0658,N,00834.5652,E,0.00,,090911,,,A*7E";
    unsigned char checksum[] = "00";
    char data[82];
    int length = strlen(nmea);
    int k = 0;
    int i;
    unsigned char XOR;

    checksum[0] = nmea[(length-2)];
    checksum[1] = nmea[(length-1)];

    for(i=1;i < (length-3);i++){
        data[(i-1)] = nmea[i];
    }
    int dataLength = strlen(data);

    for (XOR = 0, i = 0; i < dataLength; i++)   //XORer for å finne checksum
        XOR ^= (unsigned char)data[i];

    printf("*******************************************************\n");
    printf("Calculating checksum...\n");

    printf("Read checksum: %s\n",checksum);
    printf("Read data: %s\n",data);
    printf("Calculated checksum: %X \n",XOR);

    if(strcmp(XOR,checksum) == 0){          //sammenligner checksumer.
        printf("Checksum: OK!\n");
        //return 1;
    }
    else{
        printf("Checksum: Mismatch!\n");
        //return 0;
    }

    printf("*******************************************************\n");
    //nmeachecksum(buf);
    return 0;
}

Any help is greatly appreciated!

Answer 1

char XOR[2] = { 0, 0 };

And then just use XOR[0] everywhere.

The above is just my no-segfault rewrite of what your code was actually trying to do.

What it should do . . . the strcmp() is comparing binary text against a formatted version of the same value, so it won’t work. Your unsigned char XOR; (or perhaps an 8-bit <stdint.h> type) is about right. But compare this with == as a scalar instead of with strcmp().

What you compare it to . . . you will need to turn your NMEA printable hex into a scalar operand suitable for == so use sscanf() or just open code the hex conversion.¹

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^{1. Hex input conversion code examples are available in many stackoverflow answers.}