Replacing a part of a string with an other???

This is a discussion on Replacing a part of a string with an other??? within the C Programming forums, part of the General Programming Boards category; Hey all, I have a string1: "This is the string" and I want to replace the word "the" with string2: ...

  1. #1
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    Question Replacing a part of a string with an other???

    Hey all,

    I have a string1: "This is the string"
    and I want to replace the word "the" with string2: "not a"
    so that string1 becomes "This is not a string"

    i know how to use strstr to find the word i want to replace, but i don't know how to actually replace the word with the other string.

    How do i do this?

    Thanks

  2. #2
    The larch
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    Since "not a" is 5 characters and "the" is 3 characters, you'll need to move everything that follows (" string") forward by 2 characters, ensuring that the string is large enough. Then you can write "not a" where "the" is.
    I might be wrong.

    Thank you, anon. You sure know how to recognize different types of trees from quite a long way away.
    Quoted more than 1000 times (I hope).

  3. #3
    Jack of many languages Dino's Avatar
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    When you use strstr, and it is successful, it will return a pointer to "the". With this new pointer, and the pointer to the source string you searched, you can subtract the two pointers to derive the length of the first portion of the string to move into a new array.

    Then, you concat your replacement string.

    Then, you index past the position of "the" in your source string and from that point forward, concat the remaining portion of the string to the new string.

    That's telling you how to do it without telling you how to do it.

    Todd
    Mac and Windows cross platform programmer. Ruby lover.

    Quote of the Day
    12/20: Mario F.:I never was, am not, and never will be, one to shut up in the face of something I think is fundamentally wrong.

    Amen brother!

  4. #4
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    Do you like that?

    Code:
    #include <stdio.h>
    #include <string.h>
    #include <stdlib.h>
    
    char *ReplaceStrInsideString(char *ptrStr, const char *replaceStr, const char *insertStr)
    {
    	if(!ptrStr || !insertStr)
    	{
    		fprintf(stderr,"NULL input strings.\n");
    		return NULL;
    	}
    	else
    	{
    		char *nptr = NULL;
    		if((nptr = strstr(ptrStr, replaceStr)) == NULL)
    		{
    			fprintf(stderr, "Can not find \"%s\" string inside \"%s\ string.\n", replaceStr, ptrStr);
    			return NULL;
    		}
    		else
    		{
    			/* Compute final length. */
    			int nEndLen, nReplaceStartIndex;
    			/* Save the lengths that are needed. */
    			int nInsertLen = strlen(insertStr);
    			int nReplaceLen = strlen(replaceStr);
    			int nInitLen = strlen(ptrStr);
    			/* Final length of the string is known. */
    			int nFinalLen = nInitLen - nReplaceLen + nInsertLen + 1;
    			/* Pointers to strings. */
    			char *nFinalStr = NULL;
    			char *nEndStr = NULL;
    			if((nFinalStr = calloc(nFinalLen, sizeof(char))) == NULL)
    			{
    				fprintf(stderr, "Memory Allocation Error.\n");
    				return NULL;
    			}
    			/* Where is the replace string? */
    			nReplaceStartIndex = nptr - ptrStr;
    			if(nReplaceStartIndex < 0)
    				nReplaceStartIndex = -nReplaceStartIndex;
    			nEndLen = nInitLen - nReplaceStartIndex + nReplaceLen+1;
    			if((nEndStr = calloc(nEndLen, sizeof(char))) == NULL)
    			{
    				fprintf(stderr, "Memory Allocation Error.\n");
    				return NULL;
    			}
    			/* Hold the remaining part. */
    			strcpy(nEndStr, &ptrStr[nReplaceStartIndex+nReplaceLen]);
    			/* Copy characters untill the replace string. */
    			strncpy(nFinalStr, ptrStr, nReplaceStartIndex);
    			/* Copy now the insertStr. */
    			strncpy(&nFinalStr[nReplaceStartIndex], insertStr, nInsertLen);
    			/* Append the final characters. */
    			strcpy(&nFinalStr[nReplaceStartIndex+nInsertLen], nEndStr); 
    			/* Free what is unused. */
    			free(nEndStr);
    			/* Return the str. */
    			return nFinalStr;
    		}
    	}
    }
    
    /* Main. */
    int main(int argc, char *argv[])
    {
    	char *nInitString = "This is the string.";
    	char *nFinalStr = ReplaceStrInsideString(nInitString, "the", "is not");
    	printf("Initial String :\t%s\nString Replaced:\t%s\n\n",nInitString, nFinalStr);
    	printf("Hit enter to continue....");
    	getchar();
    }
    Printed Results:

    Initial String : This is the string.
    String Replaced: This is is not string.

    Hit enter to continue....

    (Well memmove can be usefull here......xmmmmmmmmmmmmm)

  5. #5
    Ex scientia vera
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    Bokarinho:

    How about hitting ENTER a few times while coding?

    Reading commented code without proper whitespace is terrible.

    EDIT:

    Also, your code has a memory leak. nFinalStr never gets freed(Sure, your OS may handle that for you, but bad practice either way).
    Last edited by IceDane; 03-23-2008 at 06:48 PM.

  6. #6
    CSharpener vart's Avatar
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    Code:
    if(nReplaceStartIndex < 0)
    	nReplaceStartIndex = -nReplaceStartIndex;
    this code suppose to do some good?

    also you do not need to allocate and free nEndStr
    You could copy the end of string from the original string

    and because you do not modify it char *ptrStr should be declared as const
    as well as char *nInitString
    The first 90% of a project takes 90% of the time,
    the last 10% takes the other 90% of the time.

  7. #7
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    Sure there is a memory leak as i am not freeing the memory used, OS can handle it properly but ok you are right. Secondly about the comments this is C commenting and it is my way of writing so i dont bother. Thirdly yes you can not use the nEndStr and this can be easily avoided and this is the only thing i agree with. But if you want to put yourself cleverer write down your own code and i will comment it too. What i ve done is to provide the user with an answer so to have a point in C how to do it. You are far better....

    Thank C programmers...

  8. #8
    CSharpener vart's Avatar
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    What i ve done is to provide the user with an answer so to have a point in C how to do it.
    Giving the learning person bad answer is worse than not giving any answer at all...

    If you are trying to teach bad practices on these forums - you should be aware to get adecvate responses about your mistakes...
    The first 90% of a project takes 90% of the time,
    the last 10% takes the other 90% of the time.

  9. #9
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    Give me your good practice......

    Bad practices.....
    XAXAXAXA!!!!!

  10. #10
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    Bad practice beacause i got a bit more memory for the nEndStr haaa?

    OK, give me a break dude, God of C....

  11. #11
    Just Lurking Dave_Sinkula's Avatar
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    Quote Originally Posted by pseudonoma View Post
    How do i do this?
    Here's a trip down memory lane:
    Find and Replace Text Function
    7. It is easier to write an incorrect program than understand a correct one.
    40. There are two ways to write error-free programs; only the third one works.*

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