Thread: unable to pass values to struct as a byte.

Hi,

I am using a struct and tying to send values to it as byte value

Code:

#include<stdio.h>


typedef struct{
    unsigned r1:1;
    unsigned r2:1;
    unsigned r3:1;
    unsigned r4:1;
    unsigned r5:1;
    unsigned dummy:3; // empty port
}rangeflags;


rangeflags Range;


int main()
{
    Range.r1 = 1;
    printf("%d%d%d%d%d\n",Range.r1,Range.r2,Range.r3,Range.r4,Range.r5);
    Range = 0b00100000;
    //Range = 0x20;
    printf("%d%d%d%d%d\n",Range.r1,Range.r2,Range.r3,Range.r4,Range.r5);
}

Error:
error: invalid suffix "b00100000" or incompatible types in assignment

I am able to access the member as Range.r1 = 1; and have no problems.
I want to send data whole at once, but how ?

Only compilers aimed specifically at the embedded microprocessor market recognise "0b" as indicating a binary constant. It is not a standard feature.

Originally Posted by Salem

Only compilers aimed specifically at the embedded microprocessor market recognise "0b" as indicating a binary constant. It is not a standard feature.

TinyCC have such feature and compile x86 exe.

Originally Posted by zub

TinyCC have such feature and compile x86 exe.

As does gcc, but the point remains that it is non-standard thus such implementations are compiler specific language extensions, hence the error that raadys encountered.

Depending on what compiler you're using, it might also be helpful to include <stdint.h> and use uint8_t instead of unsigned char. There is no guarantee that char will be a single byte. On the other hand, there's no guarantee that uint8_t will exist either (systems where the smallest addressable bit of memory is 16-bits wide, etc.), but most systems that you're likely to encounter have an 8-bit type, and uint8_t will be supported. Note that this only works if your compiler supports the C99 or later standard(s).

Originally Posted by Elkvis

There is no guarantee that char will be a single byte.

It is guaranteed that char will be a single byte, but what isn't guaranteed is that the notion of a byte will correspond to the conventional notion of an 8-bit byte. On the other hand, CHAR_BIT is guaranteed to be at least 8, so there might not be a problem, though I'm not sure if alignment or something could be an issue.

Originally Posted by laserlight

but what isn't guaranteed is that the notion of a byte will correspond to the conventional notion of an 8-bit byte.

good point.