How do i declare a byte variable?

[Manuel]

hi,

I have a problem, a stupid problem. I can't declare a variable of type
byte.

The g++ said that i have syntactic error in this line. The code is
this: byte * variable;

well, i think that the mistake is a stupidity but i don't find it.
where is it?

[Thomas Tutone]

Re: How do i declare a byte variable?

Manuel wrote:

hi,
>
I have a problem, a stupid problem. I can't declare a variable of type
byte.
>
The g++ said that i have syntactic error in this line. The code is
this: byte * variable;
>
well, i think that the mistake is a stupidity but i don't find it.
where is it?

Standard C++ doesn't have a built-in type called "byte." Just use a
char or, possibly, an unsigned char.

Try this:

char* variable1;
unsigned char* variable2;

Or perhaps you need to tell us more about what you intend to do with
the variable.

Best regards,

Tom

[David Harmon]

Re: How do i declare a byte variable?

On 10 Aug 2006 13:57:01 -0700 in comp.lang.c++, "Manuel"
<mfc1981@gmail. comwrote,

>I have a problem, a stupid problem. I can't declare a variable of type
>byte.
>
>The g++ said that i have syntactic error in this line. The code is
>this: byte * variable;

A byte in C++ is char, or unsigned char, or signed char.

But your variable above would not be a byte an any case. It would
be a pointer. If you are asking what is a byte, you should probably
avoid bytes and pointers for now and use std::string etc..

[Manuel]

Re: How do i declare a byte variable?

ouch, iam stupid ;(

well, I thought about using the variable of type byte because I need to
store values from 0 to 255.
I think that i can use this:

Thomas Tutone wrote: typedef unsigned char byte;
So this way i can use byte.

Thank you for your help.

Bye.
Manuel Fernadez Campos

Manuel wrote:

hi,

I have a problem, a stupid problem. I can't declare a variable of type
byte.

The g++ said that i have syntactic error in this line. The code is
this: byte * variable;

well, i think that the mistake is a stupidity but i don't find it.
where is it?

>
Standard C++ doesn't have a built-in type called "byte." Just use a
char or, possibly, an unsigned char.
>
Try this:
>
char* variable1;
unsigned char* variable2;
>
Or perhaps you need to tell us more about what you intend to do with
the variable.
>
Best regards,
>
Tom

[Default User]

Re: How do i declare a byte variable?

Manuel wrote:

ouch, iam stupid ;(

Please read the information below.




Brian

--
Please don't top-post. Your replies belong following or interspersed
with properly trimmed quotes. See the majority of other posts in the
newsgroup, or the group FAQ list:
<http://www.parashift.c om/c++-faq-lite/how-to-post.html>

[Frederick Gotham]

Re: How do i declare a byte variable?

Manuel posted:

well, I thought about using the variable of type byte because I need to
store values from 0 to 255.

C++ has a series of integer types, all of which come in a signed and
unsigned flavour:

char
short
int
long

The fundamental differences between them are:

(1) Their range:

rangeof(signed char) is a subset of rangeof(signed short),
which is a subset of rangeof(signed int), which is a subset of rangeof
(signed long).
rangeof(unsigne d char) is a subset of rangeof(unsigne d short),
which is a subset of rangeof(unsigne d int), which is a subset of rangeof
(unsigned long).

Note that this does not forbid them from all having the same range -- the
following could very well be true on a given system:

rangeof(signed char)==rangeof( short)==rangeof (int)==rangeof( long)

Note though that it's possible that the upper limit of "unsigned char" be
higher than the upper limit of "long".

(2) The amount of memory they occupy.

Put quite simply:
sizeof(signed char) <= sizeof(short) <= sizeof(int) <= sizeof(long)

(3) How efficiently the system deals with them (i.e. how fast it can work
with them)

The fastest type should be int, as it's supposed to be the "natural"
integer size for the system.

Now that we know a few differences between the integer types, we can make
an educated decision as to which to use for each purpose. Before we go any
further however, we should note that the Standard guarantees a minimum
range for each type:

(1) unsigned char : 0 through 255
(2) unsigned short : 0 through 65 535
(3) unsigned int : 0 through 65 535
(4) unsigned long : 0 through 4 294 967 295

(1) signed char: -127 through 127
(2) signed short: -32 767 through 32 767
(3) signed int: -32 767 through 32 767
(4) signed long: -2 147 483 647 through 2 147 483 647

The first thing to consider is whether we shall be storing negative
numbers; if so, we want a "signed" type. The first choice should be "signed
int" or "unsigned int":

int i = -3;

unsigned j = 5;

The next thing to consider is whether the number we store might fall
outside the guaranteed range of "signed int" or "unsigned int". If it does,
then we should "unsigned long" or "signed long":

long i = -70000;

long unsigned i = 70000U;

(If you're writing a positive integer literal which is larger than 65 535,
then append "U" to it.)

If the number is within range of "int" or "unsigned", then the last thing
to consider is whether memory is scarce. If we want to define an array of
87 thousand integers, we might consider using a "char" or a "short" -- it
will be less efficient, but it will use only half or a quarter of the
memory (depending on the system).

One last thing: If you don't specify the signedness of a type, then it
defaults to signed (i.e. "long" == "long signed"). However this isn't quite
true for "char". A plain char might be signed or unsigned, depending on the
system, so it isn't any use for doing arithmetic or storing numbers; it
should only be used for storing characters. If you want a signed char, then
make sure you specify "signed":

char unsigned a = 5; /* This is unsigned */

char signed b = -5; /* This is signed */

char c = 2; /* This could be either */

If you really want to become expert at working with integer types in C and
C++, then you might also want to learn about "integer promotion".

To answer your question though: If you want to store a number in the range
0 through 255, then just use "unsigned":

unsigned i = 255;

Only consider using "char" or "short" if memory is scarce, e.g.:

char unsigned array[99999999];

--

Frederick Gotham

[Frederick Gotham]

Re: How do i declare a byte variable?

Frederick Gotham posted:

(If you're writing a positive integer literal which is larger than 65
535, then append "U" to it.)

Actually, that's only necessary if the value is greater than 2 147 483 647.

The following is guaranteed to work fine on every system:

unsigned i = 2147483647;

The following might result in an ill-formed program on some systems (because
the signed integer literal might be out of range):

unsigned i = 2147483648;

Therefore, it's wise to append U to it:

unsigned i = 2147483648U;

--

Frederick Gotham

[Howard]

Re: How do i declare a byte variable?


"Frederick Gotham" <fgothamNO@SPAM .comwrote in message news:2bOCg.1251 5

>
To answer your question though: If you want to store a number in the range
0 through 255, then just use "unsigned":
>
unsigned i = 255;
>
Only consider using "char" or "short" if memory is scarce, e.g.:
>
char unsigned array[99999999];
>

Why? I'd probably use "unsigned char", especially if I was porting Pascal
code or something. That's most likely what was meant by "byte", don't you
think?

-Howard

[Frederick Gotham]

Re: How do i declare a byte variable?

Howard posted:

>To answer your question though: If you want to store a number in the
>range 0 through 255, then just use "unsigned":
>>
> unsigned i = 255;

Why? I'd probably use "unsigned char", especially if I was porting

Pascal

code or something. That's most likely what was meant by "byte", don't

you

think?

The extra efficiency of "unsigned int" is worth the cost of using up
another three bytes (or thereabouts).

Even if I were to write:

char unsigned i = 255;

, then it would still probably consume 4 bytes (or thereabouts) on most
systems.(If you have a system which can only access 4 bytes of memory at a
time, rather than one sole byte, then it would be efficient to store the
byte value in the least significant byte of the 4 bytes, and to just ignore
the values of the subsequent 3 bytes).

An easy test for this is the following:

#include <stdio.h>

int main(void)
{
struct FourBytes { char a,b,c,d; };

switch(sizeof(s truct FourBytes))
{
case sizeof(char[4]):
puts("Packed nice and tight!");
break;

case sizeof(int[4]):
puts("Aligned for efficient access.");
break;

default:

puts("Something funky's going on...");
}

return 0;
}

Notwithstanding any of this, your char is going to be promoted to int every
time you lay a finger on it.

--

Frederick Gotham

[Frederick Gotham]

Re: How do i declare a byte variable?

Frederick Gotham posted:

<snip C code>

Forgot I was posting to comp.lang.c++ (rather than comp.lang.c) -- I would
have written C++-style code if I had realised.

Nonetheless, the code is also valid C++ code (with deprecated features
albeit).

--

Frederick Gotham

[Clark S. Cox III]

Re: How do i declare a byte variable?

On 2006-08-10 18:20:25 -0400, Frederick Gotham <fgothamNO@SPAM .comsaid:

Frederick Gotham posted:
>

>(If you're writing a positive integer literal which is larger than 65
>535, then append "U" to it.)

>
>
Actually, that's only necessary if the value is greater than 2 147 483 647.
>
The following is guaranteed to work fine on every system:

No it isn't. There are many systems out there with a type unsigned that
can only represent values up to 65535

unsigned i = 2147483647;
>
The following might result in an ill-formed program on some systems
(because the signed integer literal might be out of range):
>
unsigned i = 2147483648;
>
Therefore, it's wise to append U to it:
>
unsigned i = 2147483648U;

--
Clark S. Cox, III
clarkcox3@gmail .com

[Frederick Gotham]

Re: How do i declare a byte variable?

Clark S. Cox III posted:

No it isn't. There are many systems out there with a type unsigned that
can only represent values up to 65535

"long" must have at least the following range:

-2147483647 through 2147483647

"unsigned long" must have at least the following range:

0 through 4294967295

Sounds like these systems you mention are not Standard-compliant.

--

Frederick Gotham

[Thomas Matthews]

Re: How do i declare a byte variable?

Manuel wrote:

ouch, iam stupid ;(
>
well, I thought about using the variable of type byte because I need to
store values from 0 to 255.
I think that i can use this:
>
Thomas Tutone wrote: typedef unsigned char byte;
So this way i can use byte.
>
Thank you for your help.
>
Bye.
Manuel Fernadez Campos
>
>

>>Manuel wrote:
>>

>>>hi,
>>>
>>>I have a problem, a stupid problem. I can't declare a variable of type
>>>byte.
>>>
>>>The g++ said that i have syntactic error in this line. The code is
>>>this: byte * variable;
>>>
>>>well, i think that the mistake is a stupidity but i don't find it.
>>>where is it?

>>
>>Standard C++ doesn't have a built-in type called "byte." Just use a
>>char or, possibly, an unsigned char.
>>
>>Try this:
>>
>>char* variable1;
>>unsigned char* variable2;
>>
>>Or perhaps you need to tell us more about what you intend to do with
>>the variable.
>>
>>Best regards,
>>
>>Tom

>
>

Do not use a byte variable. Use a variable that is the width of the
machine's word size that will accomodate your range. Today's computers
are optimized to handle words that are more than 8-bits wide. You
should be more concerned about the correctness and reliablity of
your program than storage requirements.

For example, the ARM7 processor is designed to handle 32-bit words.
The 8-bit quantities cause more work for the processor. Saving space
is not as important as getting the program to work correctly and
delivered on time. If the program doesn't fit in its container,
then and only then, worry about the size it occupies or the memory
it requires.


At work I am battling code that has variables declared in terms
of bits, rather than "int" or "unsigned int". When the time comes
to move to a processor with larger word size, all these variables
will have to be changed. Argggh.




--
Thomas Matthews

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[Ian Collins]

Re: How do i declare a byte variable?

Frederick Gotham wrote:

Clark S. Cox III posted:
>
>

>>No it isn't. There are many systems out there with a type unsigned that
>>can only represent values up to 65535

>
>
"long" must have at least the following range:
>
-2147483647 through 2147483647
>
"unsigned long" must have at least the following range:
>
0 through 4294967295
>
Sounds like these systems you mention are not Standard-compliant.
>

No, they are not. "unsigned" is shorthand for "unsigned int", which is
only required to represent values up to 65535.

"unsigned long" is a different type.

--
Ian Collins.

[Clark S. Cox III]

Re: How do i declare a byte variable?

On 2006-08-10 22:23:54 -0400, Frederick Gotham <fgothamNO@SPAM .comsaid:

Clark S. Cox III posted:
>

>No it isn't. There are many systems out there with a type unsigned that
>can only represent values up to 65535

>
"long" must have at least the following range:
>
-2147483647 through 2147483647
>
"unsigned long" must have at least the following range:
>
0 through 4294967295
>
Sounds like these systems you mention are not Standard-compliant.

Who said anything about "unsigned long"? The type in question was
"unsigned" (aka "unsigned int")

--
Clark S. Cox, III
clarkcox3@gmail .com