Programming This forum is for all programming questions.
The question does not have to be directly related to Linux and any language is fair game. |
Notices |
Welcome to LinuxQuestions.org, a friendly and active Linux Community.
You are currently viewing LQ as a guest. By joining our community you will have the ability to post topics, receive our newsletter, use the advanced search, subscribe to threads and access many other special features. Registration is quick, simple and absolutely free. Join our community today!
Note that registered members see fewer ads, and ContentLink is completely disabled once you log in.
Are you new to LinuxQuestions.org? Visit the following links:
Site Howto |
Site FAQ |
Sitemap |
Register Now
If you have any problems with the registration process or your account login, please contact us. If you need to reset your password, click here.
Having a problem logging in? Please visit this page to clear all LQ-related cookies.
Get a virtual cloud desktop with the Linux distro that you want in less than five minutes with Shells! With over 10 pre-installed distros to choose from, the worry-free installation life is here! Whether you are a digital nomad or just looking for flexibility, Shells can put your Linux machine on the device that you want to use.
Exclusive for LQ members, get up to 45% off per month. Click here for more info.
|
 |
10-07-2004, 03:33 PM
|
#1
|
LQ Newbie
Registered: Oct 2004
Posts: 3
Rep:
|
GCC Compilation Errors
I've created a linked list to store user data as part of a simple messenger program in C.
I'm recieiving two errors that seem simple but I'm overlooking the answer for whatever reason.
I declare a new linked list node and malloc space for it:
node *newHead;
newHead = malloc(sizeof(node));
and gcc gives a warning:assignment makes pointer from integer without a cast.
Any ideas about that one?
I also have another line, just below the previous one where I'm setting the value of a string within my node structure:
newHead->status = "Free";
and gcc gives a warning: assignment makes integer from pointer without a cast.
The structure member "status" is of type char, if that helps.
I've been away from C for like 8 months so I'm a little rusty and not that good anyways... can anybody help me?
Thanks.
The_Dish
|
|
|
10-07-2004, 04:56 PM
|
#2
|
Senior Member
Registered: Jan 2004
Location: Oregon, USA
Distribution: Slackware
Posts: 1,246
Rep:
|
Are you maybe compiling with g++ instead of gcc?
Also, the "status" member should be type char *, not char.
|
|
|
10-07-2004, 05:20 PM
|
#3
|
LQ Newbie
Registered: Oct 2004
Posts: 3
Original Poster
Rep:
|
I have no idea if its g++...
I'm telneting into a school network and I know gcc and cc are available. Both of them are giving me these errors.
Changing "status" to type char * eliminated the second error but I have a question regarding that, when and how do I determine if I want to use a char* or just a char?
Does anyone else have any idea why I would be getting an error from the malloc line?
Thanks
The_Dish
|
|
|
10-07-2004, 05:30 PM
|
#4
|
Senior Member
Registered: Jan 2004
Location: Oregon, USA
Distribution: Slackware
Posts: 1,246
Rep:
|
I get an error from malloc() when I compile with g++ and don't cast the return value. Here:
Code:
itsme@itsme:~/C$ cat sploof.c
#include <stdlib.h>
int main(void)
{
typedef struct
{
int data;
} node;
node *newHead;
newHead = malloc(sizeof(node));
return 0;
}
itsme@itsme:~/C$ gcc -Wall sploof.c -o sploof
itsme@itsme:~/C$ g++ -Wall sploof.c -o sploof
sploof.c: In function `int main()':
sploof.c:11: error: invalid conversion from `void*' to `main()::node*'
itsme@itsme:~/C$
That's with gcc-3.4.2. Older versions of g++ might give a different error.
How exactly are you compiling your program?
And to answer your question, you use char * when you want to use a pointer to type char and you use char when you want a char.
|
|
|
10-07-2004, 08:13 PM
|
#5
|
LQ Newbie
Registered: Oct 2004
Posts: 3
Original Poster
Rep:
|
I complie with:
gcc listapi.c
OR
cc listapi.c
I realize the difference between a char and a char*, I guess I just dont see when each one applies. A lot of the time in my notes from various classes, the prof's always seem to use char*'s as parameters and then randomly pick and choose between char's and char*s whenever declaring variables. But whatever, thanks for your help.
I also tried writing and compiling your code from the above reply and still recieved the same error message, so it must be the compiler at school.
The_Dish
|
|
|
10-07-2004, 08:53 PM
|
#6
|
Senior Member
Registered: Jan 2004
Location: Oregon, USA
Distribution: Slackware
Posts: 1,246
Rep:
|
You'll get the error with gcc if you don't #include <stdlib.h>. The reason is because without the malloc() prototype the return type defaults to int instead of void * like it's supposed to be. If you #include <stdlib.h> the error/warning should go away.
char and char * are definitely very much different. It would be a very lengthy topic for me to get into, but a google search on pointers in C should reveal a lot.
|
|
|
10-08-2004, 01:53 PM
|
#7
|
LQ Newbie
Registered: Oct 2004
Posts: 1
Rep:
|
It's usually a good idea to cast the return value of malloc to whatever pointer you're trying to make. A void *, which malloc returns, can't be dereferenced by itself and needs to be cast before dereferencing. I'd recommend changing your code to read:
newHead = (node *)malloc(sizeof(node));
|
|
|
10-08-2004, 04:33 PM
|
#8
|
Member
Registered: Sep 2004
Posts: 273
Rep:
|
If you code in C, it's not a good idea to cast the return value of malloc(), it's actually
a bad idea because will hide any failure to include the header where malloc() is declared,
namely stdlib.h.
In C++, on the other hand, you must cast what malloc() returns because C++ won't perform
that conversion automatically as C will. But if you use C++, you should always use new and
delete when allocating memory dynamically.
|
|
|
All times are GMT -5. The time now is 03:28 PM.
|
LinuxQuestions.org is looking for people interested in writing
Editorials, Articles, Reviews, and more. If you'd like to contribute
content, let us know.
|
Latest Threads
LQ News
|
|