extracting from a string.

Hey guys, I am learning C programming, Can someone present a program to explain this problem:

"Write a program that extracts part of the given string from the specified position.
String

Code:

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char *str[]={"Working with strings is fun"};

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"

Suppose I want to extract the word 'fun' and replace it with 'enjoy', How do I do it?

Quote:

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Write a program that extracts part of the given string from the specified position.

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That means that suppose I gave you the start position as 8 and the end position as 11 (or I told you that I wanted four characters), then you would provide me the substring "with".

Quote:

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Suppose I want to extract the word 'fun' and replace it with 'enjoy', How do I do it?

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That is a little more challenging. I suggest that you solve your current problem first.

Sorry I should have mentioned it as two problems. I will be more explicit.
1. Extract a part of a string by giving the start position and end position.
2. Search for any word in a string, if found then remove it from the string and replace it with a new word.

Sorry.

Well again, solve your first problem.

It depends on what is meant by "extract" but good practice for solving problem two, would be to copy the substring from str to interesting_part for problem one, and then physically moving the rest of the string to make room for the new word in problem two.

When you've created sufficient space, go ahead and overwrite the old word by copying the new one in.

Ah, I see. So what have you tried for part 1?

Ain't getting anything. Mam, can you please just solve the first problem for me. Please.

PART 1 ref code

Code:

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

//extract a aubstring from a given string 'src' here
//from the position start to end
//return value: the result substring
char *Substr( char *src, int start, int end );

int main(int argc, char *argv[])
{
    char *resstr = NULL;
    char *src = "aakld sdkfjlei ksd";
   
    resstr = Substr( src, 1, 3);
   
    printf("%s",resstr);
       
    system("PAUSE");       
    return 0;
}

char *Substr( char *src, int start, int end )
{
    assert( src );
   
    if( start <0 || end >= strlen( src ) )
    {
        perror("Substr():illegal index!");
        return NULL;
    }
   
    char *pstr = src+start;
    char *substr = NULL;
    int index;
   
    substr = (char *) malloc ( (end - start + 1) * sizeof( char ) );
    if(!substr)
    {
              perror("Substr():allocate memeory failed!");
              return NULL;
    }
       
    for( index =0; index <= end -start; index ++)
          substr[ index ] = pstr[ index ];
   
    substr[index] = '\0';
   
    return substr;
}

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As if by magic, an answer appears on a plate, and the OP has lost any chance of learning anything :(

At least it's bad C++, as opposed to good C, so perhaps there is still time to learn.....

Quote:

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At least it's bad C++, as opposed to good C, so perhaps there is still time to learn.....

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Code:

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string s="this is fun";
string t="fun";
string st="nofun";
s.replace(s.find(t),t.size(),st);

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:)

@OP : Try to solve the problem on your own and post your approach here. Don't expect people to write code for you.

now it's compiling! :cool:

Code:

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

//extract a aubstring from a given string 'src' here
//from the position start to end
//return value: the result substring
char *Substr( char *src, int start, int end );

int main(int argc, char *argv[])
{
    char *resstr = NULL;
    char *src = "aakld sdkfjlei ksd";
   
    resstr = Substr( src, 15, 17);
   
    printf("%s",resstr);
       
    system("PAUSE");       
    return 0;
}

char *Substr( char *src, int start, int end )
{
    char *pstr = src+start;
    char *substr = NULL;
    int index;
   
    assert( src );
   
    if( start <0 || end >= strlen( src ) )
    {
        perror("Substr():illegal index!");
        return NULL;
    }
   
   
   
    substr = (char *) malloc ( (end - start + 2) * sizeof( char ) );
    if(!substr)
    {
              perror("Substr():allocate memeory failed!");
              return NULL;
    }
       
    for( index =0; index <= end -start; index ++)
          substr[ index ] = pstr[ index ];
   
    substr[index] = '\n';
    index++;
    substr[index] = '\0';   
   
    return substr;
}

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1. char *src
should be
const char *src
because it is pointing to the string literal that cannot be changed

2. This will require to modify the
char *Substr( char *src, int start, int end );

to be

Code:

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char *Substr(const char *src, int start, int end );

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which is more correct because it does not change the src argument

3. printf("%s",resstr);
you should check the resstr before printing it, passing NULL pointer to printf will cause the crash

4. you need to free the allocated memory at the end

5. Do not cast malloc in C - read FAQ

6. ANSI C does not allows C++ style comments

Don't forget to add some start > end tests as well.