size of data types in c standard

I have a few doubts that is not clear after searching much

1. Does the size of data type depend on compiler and target? or Is it already fixed in C standards?
2. Do the short / long modify the size of the data type? What does short/long state in C standards?

What do you think about it?

The size varies with the compiler and target.

I use the standard int (stdint) types to avoid confusion,
uint8_t is unsigned 8 bits
uint32_t is unsigned 32 bit.

Mike.

jab99407 said:

1. Does the size of data type depend on compiler and target? or Is it already fixed in C standards?
2. Do the short / long modify the size of the data type? What does short/long state in C standards?

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Only minimum sizes are defined - CPUs that can handle larger sizes with no overheads may use compilers that use larger bit lengths than the minimum; eg. it's possible a char, short int and int could all be 16 bit with some compilers, or even 32 bit.

Plus different compilers have different "endedness", storing bytes low to high or high to low within words or memory addresses.

You can use sizeof() to find how big a type is within a program, and simple tests to determine endedness, if that would matter.

As Pomie says, using a library such as stdint puts numeric range restrictions on numeric types - but there is no absolute guarantee that the memory or register size in use may not be larger than that, on some systems.

See this for more info:

Pommie said:

The size varies with the compiler and target.

Click to expand...

rjenkinsgb said:

Only minimum sizes are defined [/URL]

Click to expand...

Thanks to both of you for confirmation. The minimum size of the data type is defined in C standards and the size of the data type depends on compiler and target.

The question below confuses me more

Do the short / long modify the size of the data type? What does short/long state in C standard?

From the off.. An int was a whole number ( regardless of size ) when the target was 8 bit we had int and char 8 bit and 7 bit as a character was 0~ 127.. the int was 0~255.. But an int was next to useless so the int became a 16 bit with two successive locations

char became 8 bit signed or unsigned .
int was then a short or along ( short was default ) 16bits or 32bits.

so if you do not specify and use int... 16bits is assumed if you use long then 32bits are used.

Why!!! I hear people cry.... Well an 8 bit micro math doubles with each size unsigned char + unsigned char is quick
long + long is a lot slower...

If the target is a 32bit mpu.. Then using a long is quicker than using an 8 bit integer... so as pommie said.. include the stdint.h and use the size that is needed in that instance.

jab99407 said:

Do the short / long modify the size of the data type? What does short/long state in C standard?

Click to expand...

There is no absolute standard, it's all down to specific compilers.
"Long" will often ensure it's 32 bit minimum.

"Short" is often ignored in standard C or taken the same as int; on a machine that used 32 bit int by default, it eg. may make it 16 bit.

Some MCU compilers have alternate uses - eg. a "short int" in the CCS compiler I use is a single bit, an "int1"; and "long" is 16 bit...

In other words, whatever compiler you use, assume nothing and RTFM - or use the stdint.h definitions and verify sizes if anything is critical.

As others have said, it depends on the compiler and the processor - I struggled for a while once, until I realised the processor I moved to used 32 bit integers while the one I moved from used 16 bit integers - I only got caught the once though