why the following string, 'str' is read-only?
char *str = "test string";
anyhow 'str' needs to be in memory. do you think, making 'str' red-only
would gain performance? or, it is right?
24  2713 
v4vijayakumar wrote: why the following string, 'str' is read-only?
char *str = "test string";
anyhow 'str' needs to be in memory. do you think, making 'str' red-only
would gain performance? or, it is right?
Character pointer `str` is /not/ read-only. You are free to assign any
other character pointer value to it. What /is/ read-only is the string
literal somewhere in memory to which `str` points.
One reason for this is that it enables embedded applications to put the
string literal into (physically) read-only memory. This may or may not
gain performance, but certainly saves RAM which in these systems tends
to command a price premium.
v4vijayakumar wrote: why the following string, 'str' is read-only?
Because the C standard says so.
(well, it says it's undefined behavior to modify a string
literal) char *str = "test string";
anyhow 'str' needs to be in memory. do you think, making 'str' red-only
str is not the same thing as "test string", str can be modified :-)
would gain performance? or, it is right?
Le 21-06-2006, v4vijayakumar <v4***********@ yahoo.com> a écrit*: why the following string, 'str' is read-only?
char *str = "test string";
Because that is the way the langage is defined ?
You could wonder why the langage is designed this way.
I was not there, but my few knoledges in compilation let
me assume that, for some compiler, it was easier to do
so (it allow to store it in read-only memory).
Marc Boyer
Vladimir Oka wrote: v4vijayakumar wrote: why the following string, 'str' is read-only?
char *str = "test string";
anyhow 'str' needs to be in memory. do you think, making 'str' red-only
would gain performance? or, it is right?
Character pointer `str` is /not/ read-only. You are free to assign any
other character pointer value to it. What /is/ read-only is the string
literal somewhere in memory to which `str` points.
One reason for this is that it enables embedded applications to put the
string literal into (physically) read-only memory. This may or may not
gain performance, but certainly saves RAM which in these systems tends
to command a price premium.
saving RAM?! anyhow still, you have to have these 12 bytes in RAM.
Marc Boyer wrote: Le 21-06-2006, v4vijayakumar <v4***********@ yahoo.com> a écrit : why the following string, 'str' is read-only?
char *str = "test string";
Because that is the way the langage is defined ?
You could wonder why the langage is designed this way.
I was not there, but my few knoledges in compilation let
me assume that, for some compiler, it was easier to do
so (it allow to store it in read-only memory).
Marc Boyer
shouldn't it be the other way? it should be easier to programmers.
Le 21-06-2006, v4vijayakumar <v4***********@ yahoo.com> a écrit*: Marc Boyer wrote: Le 21-06-2006, v4vijayakumar <v4***********@ yahoo.com> a écrit : > why the following string, 'str' is read-only?
>
> char *str = "test string";
Because that is the way the langage is defined ?
You could wonder why the langage is designed this way.
I was not there, but my few knoledges in compilation let
me assume that, for some compiler, it was easier to do
so (it allow to store it in read-only memory).
shouldn't it be the other way? it should be easier to programmers.
You could not expect C to be an 'universal' langage,
to find a C compiler for every platform *and* to require
too many things from the compiler.
So, yes, the C langage does not requires behaviors
that would be too hard/costly to implement (like a stop
of the program when dereferencing null pointer for
example, or out-of-bound array acces).
Marc Boyer
"v4vijayaku mar" <v4***********@ yahoo.com> wrote: Vladimir Oka wrote: v4vijayakumar wrote: why the following string, 'str' is read-only?
char *str = "test string";
anyhow 'str' needs to be in memory. do you think, making 'str' red-only
would gain performance? or, it is right?
Character pointer `str` is /not/ read-only. You are free to assign any
other character pointer value to it. What /is/ read-only is the string
literal somewhere in memory to which `str` points.
One reason for this is that it enables embedded applications to put the
string literal into (physically) read-only memory. This may or may not
gain performance, but certainly saves RAM which in these systems tends
to command a price premium.
saving RAM?!
In embedded devices, yes, why not? In large programs on a PC, yes, why
not, if the string isn't "test string" but a 2000-entry array of
200-character strings?
anyhow still, you have to have these 12 bytes in RAM.
Says who? You put them in ROM, of course. ROM is often cheaper than RAM.
In "normal" programs, you can put them in the executable image, save
some superfluous string copying, and eliminate duplicates.
Richard
v4vijayakumar schrieb:
Vladimir Oka wrote: v4vijayakumar wrote: why the following string, 'str' is read-only?
char *str = "test string";
anyhow 'str' needs to be in memory. do you think, making 'str' red-only
would gain performance? or, it is right?
Character pointer `str` is /not/ read-only. You are free to assign any
other character pointer value to it. What /is/ read-only is the string
literal somewhere in memory to which `str` points.
One reason for this is that it enables embedded applications to put the
string literal into (physically) read-only memory. This may or may not
gain performance, but certainly saves RAM which in these systems tends
to command a price premium.
saving RAM?! anyhow still, you have to have these 12 bytes in RAM.
No, they can safely be placed into ROM, as the compiler can assume that
you will never modify the string literal. If you do so, you invoke
undefined behaviour, so the compiler is not responsible for this. If you
want a modifiable string, use the string literal as an initializer for
an array:
char str[] = "test string";
--
Marc Thrun http://www.tekwarrior.de/
"v4vijayaku mar" <v4***********@ yahoo.com> wrote: Marc Boyer wrote: Le 21-06-2006, v4vijayakumar <v4***********@ yahoo.com> a =E9crit : why the following string, 'str' is read-only?
char *str = "test string";
Because that is the way the langage is defined ?
You could wonder why the langage is designed this way.
I was not there, but my few knoledges in compilation let
me assume that, for some compiler, it was easier to do
so (it allow to store it in read-only memory).
shouldn't it be the other way? it should be easier to programmers.
Why would it be easier for programmers? You can get the behaviour you
want using
char str[] = "test string";
and the efficient behaviour using
char *str = "test string";
Choice is good. Catering to stupid hack programmers is not good.
Richard This thread has been closed and replies have been disabled. Please start a new discussion. Similar topics | |
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