Data Types

The Basic Data Types

char  The smallest type on an architecture. Usually 8-bits wide. Sign depends on implementation.
int  The only type that the modulus operation can be applied on. At least 16-bits in size. Usually 32-bits on 32-bit systems.
float  Single precision floating point number. Typically 32-bits wide.
double  Double precision floating point number. Typically 64-bits wide, although can be analogous to float (i.e. 32-bits wide) on smaller systems such as 8-bit microcontrollers.
long double  Not normally supported on embedded platforms. 128-bits.
void  Special case data-type.

Using sizeof()

sizeof() can be used to return the number of bytes each type uses.

“There was a young man named Wight,
Who invented the thirteen bit byte.
You’ll get so much more,
from your memory, I’m sure.
But sadly your sizeof ain’t right.”

Fixed-width Integral Types

The problem with using int and all of it’s derivatives ( short int, long int, long long int , e.t.c) is that the width of the integer is platform specific. It is normally the same width as the platforms bus, but at least 16-bits. It is also called the natural width. For example, on an 8-bit system, an int will be 16 bits wide (remember, the C standard specifies it can’t be less than 16 bits). On a 16-bit platform, it will usually be 16 bits, 32 bits for a 32-bit platform, 64 bits for a 64-bit platform, and so on, you get the idea!

To write portable code, it is usually better to use fixed-width integral types.

Fixed-width integral types also need special symbols for printf() statements. These are specified in <cinttypes.h>. They begin with the lettters PRI.

Floating Point Support

Most higher-end miccontrollers and CPUs will have a hardware floating-point unit (FPU) inside them, which allows the CPU to do fast floating-point arithmetic. If you have a lower-end, cheaper microcontroller, it may not contain a FPU. In this case, you really have two options if you want to manipulate numbers with decimal precision:



Posted: June 14th, 2013 at 7:25 pm
Last Updated on: January 11th, 2018 at 8:13 am

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