invalid conversion from `unsigned char*' to `char*'

[tux88]

hello everyone,

I have downloaded "PicUSB" for Linux, which is a program that communicates with PIC18F2550 through USB (sends to the pic two numbers, waits for the result and shows it in a box). I've compiled it and it works fine, but now i'm trying to use the picusb.c and picusb.h files in another program, and it gives me the error:

PicUSB.cpp: In function ‘int SumaDosNumerosPIC(char, char)’:
PicUSB.cpp:143: error: conversión inválida de ‘unsigned char*’ a ‘char*’
Here's the code:

int SumaDosNumerosPIC (char num1, char num2)
{

   char *bytes;
   char *suma;
   
    unsigned char Estos_Bytes[3];
   bytes =&Estos_Bytes[0];
   suma = bytes;
   
    Estos_Bytes[0]=0x00;
    Estos_Bytes[1]=num1;
    Estos_Bytes[2]=num2;
return ( (int) *suma);
   
}

It's the same file used in the original program, i haven't changed it..

Thanks in advance (and sorry for my mistakes, i'm a spanish- speaker)

Picusb for linux: http://webs.ono.com/ma4826/

[mike_g]

Well for me it compiles if I cast what you are setting to bytes as a char pointer. As in:

bytes =(char*)&Estos_Bytes[0];

I'm not 100% sure if thats a good thing to be doing, but as far as I can see its ok

[dwks]

If that's the original code, verbatim, then the programmer (you?) must have been having a bad day. Here's some equivalent code:

int SumaDosNumerosPIC (char num1, char num2)
{
    return 0;
}

Presumably you or the original author meant to do something else . . .

[tux88]

No i'm not the author, but i don't think this

return ( (int) *suma);

is an error because compiling the picusb, it works.. the problem i have is when i try to use the same files including them in another program. the compiler says i have an error on this line:

suma = bytes;

(unsigned char* to char*)

[dwks]

Well, take mike_g's suggestion and try

suma = (char *)bytes;

But consider this. That function always returns 0. I can prove it. Run this program, which passes every possible value to the function.

#include <stdio.h>
#include <limits.h>

int SumaDosNumerosPIC (char num1, char num2)
{

   char *bytes;
   char *suma;
   
    unsigned char Estos_Bytes[3];
   bytes =&Estos_Bytes[0];
   suma = bytes;
   
    Estos_Bytes[0]=0x00;
    Estos_Bytes[1]=num1;
    Estos_Bytes[2]=num2;
return ( (int) *suma);

}

int main() {
    int x, y;

    for(x = CHAR_MIN; x <= CHAR_MAX; x ++) {
        for(y = CHAR_MIN; y <= CHAR_MAX; y ++) {
            if(SumaDosNumerosPIC(x, y) != 0) {
                printf("(&#37;i,%i) != 0\n", x, y);
            }
        }
    }
    
    printf("I rest my case.\n");

    return 0;
}

The only output is

I rest my case.

which means that the function always returns 0.

The output is the same with or without casts, I should imagine.

[MacGyver]

Nicely done.

[Salem]

> PicUSB.cpp: In function ‘int SumaDosNumerosPIC(char, char)’:
You wrote a C++ program, and posted in C.

Think about which language you're really wanting to use. Just because it mostly compiles doesn't make it any good.