Thread: problem with pointers

Hi, i am new to c programming. i still learning the basics. i have been trying writing simple code to get use to the commands. however i am stuck on a problem that i cannot solve. the codes are based on string manipulation.

there are 2 problems i am facing:
1)

Code:

#include<stdio.h>

 #include<string.h>

 int main(void)
 {

     char *str1 = "cprogramming";

     char *str2 = "this is new";

      printf("\n\nstr1 : %s\t\tstr2 : %s\n\n",str1,str2);

      printf("\n\nstrncpy(str1,str2,5): %",strncpy(str1,str2,5));

     getch();
  }

the program is suppose to replace the s first characters of str1 with the first 5 character of str2, the problem is each time 1 run the code, the window stops responding. However when i use

Code:

 
char str1[80]= "c programming";
char str2[80]= "this is new";

it works..

2)

Code:

#include <stdio.h>
#include <string.h>

void main (void)
{
    char *fullname, *firstname, *surname;
    printf("Enter Full Name (Surname first): ");
    gets(fullname);
    firstname = strstr(fullname," ");
    strnset(firstname,"",1);
    strncpy (surname,fullname,(strlen(fullname)-(strlen(firstname)+1)));
    printf("\n\nOutput: %s %s",firstname, surname);
    getchar();
}

Here the program was suppose to search for the space between two words entered and stores the word before the space into surname and the word after the space to firstname. but here also the windows stops responding when i run the code.

can someone help me figured where i did something wrong.

thanks.

In your first example you're trying to modify string literals. You can't they are read only.
In the second example you write into uninitialiized pointers. You have to allocate space using malloc().
Kurt

Originally Posted by laserlight

That is not correct since the last character might not be the newline character to be discarded. A similiarly concise yet correct alternative:

Code:

firstname[strcspn(firstname, "\n")] = '\0';

thanks a lot. but as i said i'm still on the basics. i think this was too much for,i didn't knew the existence of the command strcspn and fgets. i will go through more documentation on string manipulation and will try to write the program again!!!

ok, i tried to write the program again and well, i'm stuck with another problem. when i enter a name with the firstname and the surname of the same length the codes work fine but the problem comes when the length of the surname and the firstname differs. the codes works till the end but there are some additional characters with the firstname and the program stops reponding. i can't figure why.

Code:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

/***the purpose of this program is to search for the space between the two word entered, set
firstname to the word before the space and set surname to the word entered after the space***/

void main ()
{
    char *fullname=malloc(sizeof(fullname)),*firstname=malloc(sizeof(firstname)),*surname=malloc(sizeof(surname));
    int lengthfullname,lengthfirstname,lengthsurname;
    printf("Enter Full Name: ");
    gets(fullname);
    if (fullname == NULL) {
        printf("\n\nout of memory\n\n");
    }
    else {
        surname = strstr(fullname," ");
        lengthfullname  = strlen(fullname);
        lengthsurname = strlen(surname);
        lengthfirstname = (lengthfullname - lengthsurname);
        firstname = strncpy(firstname,fullname,lengthfirstname);
        surname = strcpy(surname,(surname+1));
        printf("\n\nOutput: %s %s\n\n",surname, firstname);
        free (firstname),(surname),(fullname);
    }
}

Originally Posted by Neo1

You're still using gets(), don't. Use fgets().

main always returns int, so instead of void main() you should write int main(). Also, your calls to malloc only allocates sizeof(char *), which probably isn't what you want. Instead of using dynamic allocation for this, use statically allocated char arrays:

Code:

char fullname[64], firstname[32], surname[32];

i have tried static allocation before, it gives error: incompatible types when assinging to types 'char[32]' from type 'char *' while using the string commands like strstr() or strncopy() and the program don't complie..

and also thnx i change the gets() to fgets()