Question

I have a really irritating problem. This is the buffer structure i am using

typedef struct BufferDescriptor {
   char * ca_head ;    /* pointer to the beginning of character array (character buffer) */
   int capacity ;      /* current dynamic memory size (in bytes) allocated to character buffer */       
   char inc_factor;    /* character array increment factor */
   int addc_offset ;    /* the offset (in char elements) to the app-character location */
   int mark_offset ;   /* the offset (in chars elements) to the mark location */
   char r_flag;        /* reallocation flag */
   char mode;          /* operational mode indicator*/

} Buffer ;

I cannot make any changes to above code. The inc_factor is supposed to be able to take values from 0 to 255.

therefore in the function where a buffer is created, i do the following so as to ensure that the inc_factor is not negative:

Buffer* b_create(int init_capacity, char inc_factor,char o_mode){
    Buffer* buffer = (Buffer*)malloc(sizeof(Buffer));
    buffer->ca_head=(char*)malloc(sizeof(char)*init_capacity);

    buffer->inc_factor=(unsigned char)(inc_factor);

But the following line gives out a negative number:

printf("inc factor = %d",buffer->inc_factor);

What am I doing wrong here ? Plz Help.

Answer 1

You are formatting a signed variable as a signed value, so of course it will output a negative value if the variable exceeds 127. That is what happens when you store an unsigned value into a signed variable – it wraps around to the negative. If you cannot change the variable type itself, then you have to change how it is being formatted (type-casting a signed value to an unsigned type and then assigning to a signed variable is pointless):

printf("inc factor = %u", (unsigned char) buffer->inc_factor); 

Or:

printf("inc factor = %d", (unsigned char) buffer->inc_factor);