字符到字节签名

Question

I have a binary file written in C containing a signed char data type equal to the number 1. I read in the single byte into a byte data type using MappedByteBuffer. However, when I print it out I get 49. What am I doing wrong?

C:

char * buffer = malloc(100);
signed char c;
int temp;
printf("Coordinate System?\n");
scanf("%s",&buffer[0]);
sscanf(&buffer[0],"%d",&temp);
c = temp+'0';
fwrite(&c,1,1,fd);

Java:

byte b;
b = file.read();
System.out.println(b) ===> prints the number 49.        

I know it is some kind of bit order or something but I am not sure.

Thanks

Answer 1

The issue is with:

sscanf(&buffer[0],"%c",&c);

it says to scan the incoming character as an ascii value. so you can type 'a', '-', or '1' and the ascii value will be scanned.

you would need to scan %d instead to get an actual integer. you would scan into an int variable instead of a char, then do a 0-255 range check to determine if it's viable to store in a single byte.