search a string...

This is a discussion on search a string... within the C Programming forums, part of the General Programming Boards category; Hi all, i have a problem.. i want to search a string say "abc" from a file and replace this ...

  1. #1
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    search a string...

    Hi all,
    i have a problem.. i want to search a string say "abc" from a file and replace this string with say "xyz" can anyone help me to do this....please gimme some tips or sample codes...
    thanks....

  2. #2
    CSharpener vart's Avatar
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    easiest way (for not to big files
    read the whole file into buffer
    append 0 at the end
    use strstr to locate the string
    replace it with another string
    write buffer back to file
    The first 90% of a project takes 90% of the time,
    the last 10% takes the other 90% of the time.

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    Thanks vart,
    i have already done the same thing.... but i am not able to get how to replace the string..... i have used fgets() and strstr()... can u please gimme a simple code for this...

  4. #4
    {Jaxom,Imriel,Liam}'s Dad Kennedy's Avatar
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    strstr() returns a pointer to a location within the string. To replace it, you'd do a memcpy() or loop through one char at a time from apointer[0] - apointer[strlen() - 1].

  5. #5
    CSharpener vart's Avatar
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    hope - this will help
    Code:
    #include <stdio.h>
    #include <string.h>
    
    int main()
    {
    	char buffer[]="123abc789";
    	char* p = strstr(buffer,"abc");
    	if(p)
    	{
    		strncpy(p,"456",3);
    	}
    	printf("%s",buffer);
    	return 0;
    
    }
    
    /*
    My output
    123456789
    */
    The first 90% of a project takes 90% of the time,
    the last 10% takes the other 90% of the time.

  6. #6
    {Jaxom,Imriel,Liam}'s Dad Kennedy's Avatar
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    vart, shame on you for doing compile's homework!!!

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    Thanks vart,
    and thanks kennedy too....
    kennedy this is not a home work... and i am a professional in electronics and communications... but i am a begginer in "C"... thats y asking help with u people..hope u will make me a good "C" programmer too...

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    Hi friends once again some clarifications....
    in the above program.... if the search string is say "gram" and if that string is not there but if there is a string "program" then it says the string found... how to overcome this. .that is adding a space before and after the string.. ???
    thanks..

  9. #9
    Registered User ssharish2005's Avatar
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    Code:
    #include <stdio.h>
    #include <string.h>
    
    int main()
    {
        char str[] = "This is a test pro gram";
        char search[] = "gram";
        char *p;
        
        p = strstr(str,search);
        
        printf("Serach string -> %s\n",str);
        
        if((*(p-1) == ' ') && (*(p + strlen(search)) == ' ' || *(p + strlen(search)) == '\0'))
            printf("Result : String found\n");
        else
            printf("Result : String not found\n");
        
        getchar();
        return 0;
    }
    
    /* my output
    Serach string -> This is a test program
    Result : String not found
    
    Serach string -> This is a test pro gram
    Result : String found
    */
    NOTE: you will have check for the return value str that is *p;

    Hope this will help

    ssharish2005
    Last edited by ssharish2005; 01-12-2007 at 06:49 AM.

  10. #10
    and the hat of int overfl Salem's Avatar
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    Well until you match at the start of a string at least.
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.
    I support http://www.ukip.org/ as the first necessary step to a free Europe.

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    wow thannks ssharish2005,
    thanks a lot.....

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    but one more doubt struck my mind..... say i have a very large text file.... and i want to search a string and replace there.... without making one more copy of the file.. how to do this...
    thanks...

  13. #13
    Fear the Reaper...
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    You'll likely still have to create a new output file with your modified output. Then delete the old one and rename the new one.
    Teacher: "You connect with Internet Explorer, but what is your browser? You know, Yahoo, Webcrawler...?" It's great to see the educational system moving in the right direction

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    oh.. fine.. but why cant we search and replace directly in a file itself ???
    thanks....

  15. #15
    {Jaxom,Imriel,Liam}'s Dad Kennedy's Avatar
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    You can:

    1) If the string you are replacing is the same length.

    2) If the string you are replacing is longer than the one you are inserting you'd have to move all of the remaining chars in the file up to the offset (it'd be a lot of fseek()ing but you _could_ do it).

    3) If the string you are replacing is shorter than the one you are inserting you'd have to move the EOF marker (which is already cleared) and insert the string keeping a short LIFO buffer to advance yourself through the file (again, lots of fseek()ing).

    If you notice, two of the three options above, where doable, aren't the smartest things in the world. Coping a file to memory (assuming that the file will fit into memory) then modifing it and returning it to a newly written file is MUCH easier. Even file-to-file modifications are much prefered.

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