Convert char pointer to unsigned char array

Question

I want to convert a char pointer to a unsigned char var, I thought I could do that with just casting but it doesn't work:

char * pch2;
//Code that puts something in pc2
part1 = (unsigned char) pch2;

I've the code to this:

result.part1 = (unsigned char *) pch2;
printf("STRUCT %s\n",result.part1);

result is just a struct with unsigned char arrays.

EDIT:

            pch2 = strtok( ip, "." );

            while( pch2 != NULL ){
                printf( "x %d x: %s\n", i, pch2 );
                pch2[size-1] = '\0';

                if(i == 1)
                    result.part1 = (unsigned char *) pch2;
                if(i == 2)
                    result.part2 = (unsigned char *) pch2;
                if(i == 3)
                    result.part3 = (unsigned char *) pch2;
                if(i == 4)
                    result.part4 = (unsigned char *) pch2;
                i++;
                pch2 = strtok (NULL,".");
            }   
            printf("STRUCT %c\n",result.part1);

Struct:

typedef struct
{
    unsigned char part1;
    unsigned char part2;
    unsigned char part3;
    unsigned char part4;
} res;

In your title you ask for an array, in your text for a variable and most of the answers are showing you how to get a pointer to unsigned char. Which is it? — dmckee --- ex-moderator kitten
– dmckee --- ex-moderator kitten, Commented Nov 25, 2012 at 18:02
I'm having a pointer that I want to convert to a unsigned char array? — user1007522
– user1007522, Commented Nov 25, 2012 at 18:04

iabdalkader · Accepted Answer · 2012-11-25 19:03:19Z

3

you cast to unsigned char not unsigned char* you forgot the *

part1 = (unsigned char*) pch2;

if pch2 is not null terminated the program will crash, if you're lucky, when you use strlen, so you need to null terminate it first before printing using pch2, try this instead:

pch2[size-1] = '\0';  /* note single quote */
result.part1 = (unsigned char *) pch2;

Update: define your structure like so:

typedef struct
{
    const char *part1;
    const char *part2
    const char *part3;
    const char *part4;
} res;

And assign to it without casting at all:

result.part1 = pch2;

edited Nov 25, 2012 at 19:03

answered Nov 25, 2012 at 17:56

iabdalkader

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13 Comments

user1007522 Over a year ago

when printing out like a string the program stops running?

iabdalkader Over a year ago

@user1007522 C strings should be null terminated strings of char not unsigned characters, what are you trying to do exactly ?

Lie Ryan Over a year ago

@user1007522: you can print a single char using %c. For example: printf("STRUCT %c\n", *result.part1);

user1007522 Over a year ago

Thanks when using %c it works like a charm. Do I need a for loop then to print everything?

iabdalkader Over a year ago

@user1007522 no, you need to NULL terminate the string pch2[size-1]=0

|

piokuc · Accepted Answer · 2012-11-25 17:56:58Z

1

You want to do this:

part1 = (unsigned char*) pch2;

Instead of:

part1 = (unsigned char) pch2;

answered Nov 25, 2012 at 17:56

piokuc

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Comments

Rahul Tripathi · Accepted Answer · 2012-11-25 17:58:11Z

1

Try something like this:-

 char *ph2;
 unsigned char *new_pointer = (unsigned char*) ph2;

answered Nov 25, 2012 at 17:58

Rahul Tripathi

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2 Comments

user1007522 Over a year ago

I've done that, but when doing a printf %s the program stops? Is it something with strtok because pch2 is init by strtok ?

Rahul Tripathi Over a year ago

You can try with printf("STRUCT %c\n",result.part1);

Maciek · Accepted Answer · 2012-11-25 18:55:54Z

1

I want to convert a char pointer to a unsigned char var

Are you sure? Converting pointer to char to unsigned char is not going to do any good - value will get truncated to 1 byte, and it will be meaningless anyway. Maybe you want to dereference a pointer and get value pointed by it - then you should do something like this:

unsigned char part1 = (unsigned char)*pch2;

After your edit I see that part1 is character array - if your program crashes after it is used, you probably fill pch2 incorrectly. Maybe you forgot '\0' terminator?

EDIT:

You see, it is much better now to answer your question having all required information. Do you need to use strtok? Would this be good?

    res result;
    char* ip = "123.23.56.33";

    sscanf(ip, "%hhu.%hhu.%hhu.%hhu", &result.part1, &result.part2, &result.part3, &result.part4);

edited Nov 25, 2012 at 18:55

answered Nov 25, 2012 at 18:05

Maciek

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8 Comments

dmckee --- ex-moderator kitten Over a year ago

I think this is closer to what the OP is looking for than the answers to date, but I'm still not sure the OP has been clear yet.

user1007522 Over a year ago

I've edited the code, I terminated the char array, like you see the first print of pch2 works like a charm. The last one not :(

Maciek Over a year ago

crucial point here is - what is pointed by pch2 and how it gets there. Without knowing this, we cannot tell whether it is constructed correctly. Your way of terminating string is incorrect - "\0" definitely is not what should be there, and anyway you are calling strlen on potentially incorrect string. We need to know what value pch2 points to.

user1007522 Over a year ago

No, I can use sscanf, but the code crashes when Copy your line. Also my struct is not a unsigned char * x but just unsigned char x or that doesn't matter with the adress operator.

Maciek Over a year ago

Then it would be helpful to see what is result structure and its part1...part4 members.

|

user1007522 · Accepted Answer · 2012-11-25 21:32:50Z

0

Found the problem, forgot to cast the char pch2 to unsigned int and then I can printout with %u. Code:

unsigned int temp;

temp = atoi(pch2);

result.part1 = temp;
printf("Struct: %u\n",result.part1);

Thanks for your help guys!

answered Nov 25, 2012 at 21:32

user1007522

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