Thread: strings

Im trying to make a few basic functions for string manipulation.

I get errors when I try to return a string from a function.

Code:

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

#define COLS 80
#define ROWS 80

char right(char [], int);
//char left(char [], int);

int main() { 
  char string[ROWS];
  int n;

  printf("\nEnter in a string.");
  printf("\n:");

  gets(string);
  
  printf("\nEnter in a number to cut out of string.");
  printf("\n:");
  scanf("%d", &n);

  printf("\nString cut to right: %s", right(string, n));
  //printf("\nString cut to left: %s", left(string, n));

  return 0;
}

char right(char string[], int n) {
  char newString[ROWS];
  int ih, i = 0, j = 0;

  if((int)strlen(string) < n) {
    return string;  /* error here */
  }
  ih = strlen(string) - n;

  while(i<(int)strlen(string)) {
    if(i >= ih) {
      newString[j] = string[i];
      j++;
    }
    i++;
  }
  
  newString[j] = '\0';

  return newString;  /* error here */
}

The reason you're getting an error is because you're returning a local variable, which is destroyed when the function goes out of scope.

Change this:
> char newString[ROWS];

To these two lines:

char newString[ROWS];
char *s = NULL;


Change this:

> newString[j] = '\0';
>
> return newString; /* error here */

To this:

newString[j] = '\0';
s = malloc( strlen( newString ) +1 );
strncpy( s, newString, strlen( newString ) );
return s;

Now what you've just done is duplicated the contents in the buffer "newString", and put it in an allocated block of memory which you return via a pointer to it.

Quzah.

still have problems.

Code:

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

#define COLS 80
#define ROWS 80

char right(char [], int);
//char left(char [], int);

int main() { 
  char string[ROWS];
  int n;

  printf("\nEnter in a string.");
  printf("\n:");

  gets(string);
  
  printf("\nEnter in a number to cut out of string.");
  printf("\n:");
  scanf("%d", &n);

  printf("\nString cut to right: %s", right(string, n));
  //printf("\nString cut to left: %s", left(string, n));

  return 0;
}

char right(char string[], int n) {
  char newString[ROWS];
  char *s = NULL; 
  int ih, i = 0, j = 0;

  if((int)strlen(string) < n) {
    s = malloc(strlen(string)+1); 
    strncpy(s, string, strlen(string)); 
    return s;				/* error here */
  }
  ih = strlen(string) - n;

  while(i<(int)strlen(string)) {
    if(i >= ih) {
      newString[j] = string[i];
      j++;
    }
    i++;
  }
  
  newString[j] = '\0';

  s = malloc(strlen(newString)+1); 
  strncpy(s, newString, strlen(newString)); 
  return s;				/* error here */
}

char right(char string[], int n) {

This should be a pointer to a character.

char *right( ... )

Quzah.

Final form looked like this:

Code:

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

#define COLS 80
#define ROWS 80

char *right(char [], int);
char *left(char [], int);

int main() { 
  char string[ROWS];
  int n;

  printf("\nEnter in a string.");
  printf("\n:");

  gets(string);
  
  printf("\nEnter in a number to cut out of string.");
  printf("\n:");
  scanf("%d", &n);

  printf("\nString cut to right: %s", right(string, n));
  printf("\nString cut to left: %s", left(string, n));

  return 0;
}

char *right(char string[], int n) {
  char *newString;
  int ih;

  if((int)strlen(string) < n) {
    return string;
  }
  ih = strlen(string) - n;
  newString = &(string[ih]);

  return newString;
}

char *left(char string[], int n) {
  char *newString;

  if((int)strlen(string) < n) {
    return string;
  }
  string[n] = '\0';
  newString = &(string[0]);

  return newString;
}

/* e.g.: othello is passed with a 5, othello size is 7
** 7 < 5 keep going
** ih = 7 - 5, ih = 2
*/