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: Per W. <pw...@ia...> - 2007-05-07 13:32:10
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Note that strdup() can be used to both allocate memory for a string, and
copy the string data to the allocated buffer.
/pwm
On Mon, 7 May 2007, Jan Mura wrote:
> Oh God, thank you. It is enough for today I think.
>
> Jan Mura
> ----- Original Message -----
> From: "Jonathan Winterflood" <jon...@gm...>
> To: "Jan Mura" <jan...@vo...>
> Cc: "Per Westermark" <pw...@ia...>; "Philip Bennefall"
> <phi...@pb...>; <dev...@li...>
> Sent: Monday, May 07, 2007 12:32 PM
> Subject: Re: [Dev-C++] Casting of int to string
>
>
> > 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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> > > > >
> > > > > --
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> > > > >
> > > > >
> > > >
> > > >
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> >
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