Thread: hex and binary functions

You expect that character to hold that string? sprintf's first argument is a char * not a char.

That's because you return a pointer to a region of memory that goes out of scope as soon as the function ends. To make a long story short, allocate memory in the calling function and pass a pointer to this memory as a parameter to your function.

[edit]

Code:

#include <stdio.h>

char* tohex(char *dst, char val)
{
   sprintf(dst, "0x%X", (unsigned)(unsigned char)val);
   return dst;
}

int main(void)
{
   char hexval[10], value = 'A';
   puts(tohex(hexval, value));
   return 0;
}

/* my output
0x41
*/

hexval is local to (the stack frame of) the function. after the function returns, the frame is 'destroyed' and the address returned is invalid. pass a pointer to a character array large enough to hold the data to the function and it should work.

Thanks guys and now that I have tested it more the binary does not work correctly. I will keep working and post here again if I have problems. Thanks again!
~Sven

EDIT~
I ran into problems on the binary one already. I dont get any errors on the function itself but when I call it inside the main function I get an error. Here is all of the code:

Code:

void tobin(char* b,int n){
     char bin[17];
     int x;
     for(x=0;x<16;x++){
                       if(n & 0x8000){
                            bin[x]='1';
                       }
                       else{
                            bin[x]='0';
                       }
                       n<<=1;
     }
     bin[16]='\0';
     sprintf(b,"%s",bin);
     return b;
}

int main(){
   char binval[20];
   int value = 19;
   puts(tobin(binval,value));
   getchar();
   return 0;
}

The error that I get is on the bolded line in main(). The error message is "invalid use of void expression". What does that mean?
~Sven

Originally Posted by 00Sven

The error that I get is on the bolded line in main(). The error message is "invalid use of void expression". What does that mean?

It means you should look at the return type of the function tobin.

[edit]Something else to look at.

It appears that you have declared character as a string rather than a single character. Match the arguments to tohex with the prototype.

Code:

scanf("%s",character);

This is a bad way to read strings anyway.
FAQ > How do I... (Level 1) > Get a line of text from the user/keyboard (C)

Well then you didn't fix it. To read a character using scanf():

Code:

scanf("%c", &character);

Rather than using scanf() to read a single character, you would be better off using getchar().

To read a string using scanf(), use %s and drop the ampersand. A string is already a pointer. You would be better off using fgets() anyway, which is covered in the FAQ.

Besides, that's not where you error is. Your error is on this line:

Code:

printf(tohex(converted,character));

argument 2 of tohex() is a character, not a string.