Re: [Dev-C++] Casting of int to string
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Re: [Dev-C++] Casting of int to string
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From: Jonathan W. <jon...@gm...> - 2007-05-07 10:33:02
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Since the name is just a pointer, the malloc does not allocate _any_ memory
for the name, only 4 bytes(?) for the pointer.
You should seperately allocate the memory for the name, or use another
trick: allocte enough memory _after_ the structure to contain your name, in
the same malloc (this saves allocating lots of small blocks, in the case
that the name for that structure will not change)
eg:
member = malloc(sizeof(struct bet_list)+length_of_name_including_nul);
//allocate both
member->name = (char *)member + sizeof(struct bet_list); // point the name
at the memory after the structure
strcpy(member->name, name);
It might look slightly hacky, but it works fine :)
Any comments on this?
Obviously if you dno't know the size of the string before allocatingthe
struct, or it may change, you'll have to allocate them separately:
member = malloc(sizeof(struct bet_list)); //allocate just one
member->name=NULL; // for checking: malloc does not initialize data (I guess
you already know that)
member->next = NULL;
/* ... */
if (member->name) {
free(member->name); //in case you are changing names
member->name=NULL; // if you aren't going to put the name back immediately
}
member->name = malloc(strlen(name)+1); //allocate the name
strcpy(member->name, name);
Jonathan
On 5/7/07, Jan Mura <jan...@vo...> wrote:
>
>
> Thank you, it came to my mind what about the NULL character at the end of
> the string.
>
> Maybe one more thing. I am not sure if my code is ok because of the
> similar
> reasons about some illegal memory usage.
> So I have something like
>
> struct bet_list
> {
> int id;
> char *name;
> struct bet_list *next;
> };
> ...
> struct bet_list *member, *temp;
>
> member = malloc(sizeof(struct bet_list));
>
> member->id = 1;
> strcpy(member->name, "some string here");
> member->next = NULL;
>
> ...
>
> I am not sure if malloc allocates enough space if it dont know how long is
> a
> string I would like to put in.
>
> Thanks again
>
> Jan Mura
>
> ---- Original Message -----
> From: "Per Westermark" <pw...@ia...>
> To: "Philip Bennefall" <phi...@pb...>
> Cc: "Jonathan Winterflood" <jon...@gm...>; "Jan Mura"
> <jan...@vo...>; <dev...@li...>
> Sent: Monday, May 07, 2007 10:21 AM
> Subject: Re: [Dev-C++] Casting of int to string
>
>
> > Better C libraries have the snprintf() function, that takes the size of
> > the buffer as an input parameter.
> >
> > /pwm
> >
> > On Mon, 7 May 2007, Philip Bennefall wrote:
> >
> > > Sorry, I should've phrased it differently. Yup, allocating too little
> memory is a bad idea in any situation because the function has no way of
> knowing when it is supposed to stop writing. I just put 32 in there
> because
> it ensures (100 %) that the entire value will be stored including the Null
> terminator.
> > >
> > > Regards
> > > Philip Bennefall
> > > ----- Original Message -----
> > > From: Jonathan Winterflood
> > > To: Jan Mura
> > > Cc: dev...@li...
> > > Sent: Monday, May 07, 2007 9:08 AM
> > > Subject: Re: [Dev-C++] Casting of int to string
> > >
> > >
> > > Just a note:
> > > """ It basically prints your integer into the character array, as
> long
> as there is enough space to hold it """
> > > Actually it will print the integer whether there is enough space or
> not.. It is entirely Your job to make sure there is enough space, or else
> sprintf will just keep on printing in memory after the end of the array.
> Obviously this is a very bad idea, since there is other data there.
> > > In this case, determining the necessary space is as easy as 'what's
> the maximum digit count in an integer'... but in other cases, you can get
> wierd crashes, wrong data for no apparent reason, or even create an
> exploit
> in your program.
> > >
> > > Thought you might want to know that (and if you did, no offense
> intended :)
> > > Jonathan
> > >
> > >
> > > On 5/7/07, Philip Bennefall < phi...@pb...> wrote:
> > > This will do the job.
> > > char outputstring[32];
> > > sprintf(outputstring, "%d", integer);
> > >
> > > It basically prints your integer into the character array, as long
> as there
> > > is enough space to hold it. This method works both in C and C++.
> There are
> > > other methods such as stringstream, but they only work in C++. If
> you're
> > > compiling a C program, for this function to work you need to
> include
> stdio.h
> > > and for C++ it is cstdio.
> > >
> > > Regards
> > > Philip Bennefall
> > > ----- Original Message -----
> > > From: "Jan Mura" <jan...@vo...>
> > > To: <dev...@li... >
> > > Sent: Monday, May 07, 2007 8:26 AM
> > > Subject: [Dev-C++] Casting of int to string
> > >
> > >
> > > > Hello,
> > > >
> > > > I would like to compare an integer with a string using strcmp().
> So I need
> > > > to cast the int type to string (*char). Is there some commone
> way
> how to
> > > > do
> > > > it. Should I use & operator and adress of int in teh function?
> Or
> > > > something
> > > > else?
> > > >
> > > > Thank you very much
> > > >
> > > > Jan Mura
> > > >
> > > >
> > >
>
>
>
> >
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