Doubt in malloc()

[MAshokKumar]

Hi,

I have a doubt while specifying the size in malloc().

int main()
{
char *str;
str = (char *)malloc(sizeof(char) * 256);
scanf("%s", str);
}

the above program will work fine, only if the inputed strings length is less than 256. Is there anything available, which can calculate the size dynamically?

so that irrespective of the length of the inputed string, my program should work fine.

regards,
Ashok

[Philip Nicoletti]

If programming in C++, you can use std::string instead
of a char array. Stroustrup gives a solution using C-style
coding at (it is somewhat messy) :

http://www.research.att.com/~bs/new_learning.pdf

[MAshokKumar]

Thanks Philip,

I have already worked with std::string, but just wanted to know how can I do it in C. and its clear now.

Thank you very much for the quick response..

regards,
Ashok

[Guysl]

I would say the topic should be doubt in input methods rather than malloc.

Another way to deal with unexpected length of input is
reading it using 'fgets' with a length limitation
(it can be used for reading from 'stdin' too),
using 'realloc' as necessary and/or using 'sscanf' to parse the buffer.

Regards,
Guy

[Cariboo]

Another way to deal with unexpected length of input is
reading it using 'fgets' with a length limitation
(it can be used for reading from 'stdin' too),
using 'realloc' as necessary and/or using 'sscanf' to parse the buffer.

Excuse me for the question, but could you give an example, please ???

[Guysl]

Here is an example:

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


#define EXTENTSIZE 5

int main()
{
  int bufferSize = EXTENTSIZE;
  int numExtents = 0;
  char* buffer = (char*)malloc(bufferSize);

  //
  // fgets reads its second parameter's value -1 characters, or until it
  // reaches a newline, which come first.
  // since buffer is been expanded when fgets neither read a newline nor end-of-file, 
  // we must read each cycle of the loop -
  // into the starting location of the last extention which is:
  // buffer+(EXTENTSIZE-1)*numExtents
  //

  while(fgets(buffer+(EXTENTSIZE-1)*numExtents++,EXTENTSIZE,stdin)!=NULL)
  {
     // if fgets read a newline then replace it with null character
     if(buffer[strlen(buffer)-1]=='\n')
     {
        buffer[strlen(buffer)-1]='\0';
        break;
     }

     // expand buffer with EXTENTSIZE bytes:
     buffer=(char*)realloc(buffer,(bufferSize+= EXTENTSIZE));
  }

  puts(buffer);
  free(buffer);
  return 0;
}

[jolley]

Originally posted by MAshokKumar
Hi,

I have a doubt while specifying the size in malloc().

int main()
{
char *str;
str = (char *)malloc(sizeof(char) * 256);
scanf("%s", str);
}

the above program will work fine, only if the inputed strings length is less than 256. Is there anything available, which can calculate the size dynamically?

so that irrespective of the length of the inputed string, my program should work fine.

regards,
Ashok

u can get it in this way:
#include<stdio.h>
#include<stdlib.h>
int main()
{
char *str,
i;
scanf("%d",&i);
printf("%d\n",i);
str = (char *)malloc(sizeof(char) *i);
scanf("%s", str);
printf("%s\n",str);
return 0;

}