pascal to C problem in struct storing data

ngan_yine · 01-24-2005, 01:00 PM

Hi
I used to program in pascal for my school and now I am learning c by myself ;
in pascal we would call it function and it like struct in C;
I want to know why can't we initilizalite the string in this way;
struct mailing{ /*first way*/
char name[100];
int phone;
}list;
int main(){
list.name="ngan yine";
but for integer we can;
list.phone=1234466;
in pascal we usually does it in similiar way .
Is there any way we can initilizlite without working around this way below;
struct mailing{
char name[100];/*second way*/
int phone;
} list = {
"ngan yine",
12323232,};

please tell me why can't we use in first way?

itsme86 · 01-24-2005, 02:25 PM

It has nothing to do with the struct. It has to do with arrays. You can't do this either:

Code:

int main(void)
{
  char name[100];

  name = "blah";
  return 0;
}

But you can do:

Code:

int main(void)
{
  char name[100] = "blah";

  return 0;
}

If you want to do it your way then you can do this:

Code:

int main(void)
{
  char *name;

  name = "blah";
  return 0;
}

Don't try to modify the contents of name after that though, because "blah" is stored in read-only memory. Otherwise you'll have to use strcpy() to store the string in the name variable.

jtshaw · 01-24-2005, 02:45 PM

I personally always feel safer initializing all strings with strncpy.

Code:

#include <string.h>

struct mailing {
        char name[100];
        int phone;
};      

int main() {
        struct mailing *list = malloc (sizeof(struct mailing));
        
        strncpy(list->name,"ngan yine",100);
        list->phone = 1234466;
        
        /* lots more code...*/
        free(list);
        return 0;
}

strncpy lets you put bounds on how much to copy from the source to the destination. So if for some reason your source is bigger then your destination you won't end up with a segfault or bad data somewhere in your program.

itsme86 · 01-24-2005, 03:52 PM

Of course, then you always have the potential of having a non-terminated string:

Code:

#include <string.h>

int main(void)
{
  char small[5];

  strncpy(small, "too big", sizeof(small));
  // Uh oh! small contains 't' 'o' 'o' ' ' 'b'. No '\0'!

  return 0;
}

Of course adding a small[sizeof(small)-1] = '\0'; after every strncpy() call will keep you safe.

ngan_yine · 01-24-2005, 09:45 PM

Hi
Thanks guys ,That clear a few thing up;
I guess I still think as pascal programer because in pascal after declaring string as variable;
program myprogram;
var
name string;
began
name:="ngan yine";
end.
Declaring and initlizliting in such way is allow in pascal and I guess I was thinking in such way in C .I only found out that is wrong only when I tried to complie ,gcc tell me that there is incompartiable type in
certain line and I got lost untill you guy point me out;
I guess I forgot that in C the string is declare as array of char and not as string so bascially
name ="ngane yine" would be illegal to use;
But one more question ;is there any way to decare name as string in C?
like in pascal?

itsme86 · 01-25-2005, 01:48 AM

There is no such thing as a string like you're thinking of in C. In C, a string is defined as an array of characters terminated with an ASCII value 0 ('\0').

ngan_yine · 01-25-2005, 03:21 AM

Ok!
Thanks for telling me that there is no string format in C.I thought all the hight level language
have string as in pascal because is such a important feature as integer or float(in pascal we call it real);I guess I have to stop thinking in pascal and start fresh new with C.
Thanks .