about STRING in gcc

surya123 · 07-11-2003, 09:20 PM

to continue about string, pls look to this:

Code:

01#include <stdio.h>
02#include <string.h>
03
04#define STR_SIZE 70
05
06struct reckey
07{
08  char *name;
09};
11typedef struct reckey key;
12
13int main()
14{
15  char *S,*D,*T,*P,*K,A[STR_SIZE];
16  key *user;
17
18  S = "123456789 223456789 323456789 423456789 523456789 623456789\n"; 
19  //if we insert string to S with over than 32 karakter it will make strcpy(P,S) causing segment fault.
20
21  user = (key *)malloc(sizeof(key)); 
22  user->name = (char *)malloc(sizeof(char)*STR_SIZE);
23  strcpy(user->name,S);
24
25  D = S;
26  printf("%s",D);
27
28  strcpy(A,S);
29  printf("%s",A);
30
31  T = A;
32  printf("%s",T);
33
34  P = (char *)malloc(sizeof(char));  
35  strcpy(P,A);
36  printf("%s",P);
37
38  K = &A[0];  //equal with K = A;
39  printf("K=%s A=%s",K,A);
40
41  printf("user->name %s",user->name);
}

i compiled with: "gcc string.c"
run : "./a.out"
output:

123456789 223456789 323456789 423456789 523456789 623456789
123456789 223456789 323456789 423456789 523456789 623456789
123456789 223456789 323456789 423456789 523456789 623456789
123456789 223456789 323456789 423456789 523456789 623456789
K=123456789 223456789 323456789 423456789 523456789 623456789
A=123456789 223456789 323456789 423456789 523456789 623456789
user->name 123456789 223456789 323456789 423456789 523456789 623456789

why syntax strcpy() can do its job when i didnt type "#include <string.h>" in line-02?
in line-22 and line-34, if i didnt include multiply STR_SIZE, the result is ok, anyone know why? or when P = (char *)malloc(sizeof(char)) how many karakter that it preserved exactly?
For this P = (char *)malloc(sizeof(char)*10) its explanation by Dark_Helmet that i've read is very clear.thx.

my conclusions:
if we want using strcpy then the syntax is: strcpy(array,string)
examples:

Code:

char *String1, *String2, Array[STR_SIZE];
key *user;

   //to fill words/sentence from string_variable to other string_variable:

   String1 = String2; Ok
   strcpy(Array1,String1); Ok
   String1 = Array1; Ok
   String1 = Array1[0]; Ok
   String1 = (char *)malloc(sizeof(char));
   strcpy(String1,String2); Ok

   user = (key *)malloc(sizeof(key)); 
   user->name = S; Not Ok! even the result is Ok but in LIFO will cause a problem. 		(see in threads "what happen to my LIFO" and the explanation by Dark_Helmet)

   user = (key *)malloc(sizeof(key)); 
   user->name = (char *)malloc(sizeof(char)*STR_SIZE);
   strcpy(user->name,S); Ok

if anyone has opinion to my conclusions, please tell me, i need the truth understanding. i'm very grateful.