strstr() question

This is a discussion on strstr() question within the C Programming forums, part of the General Programming Boards category; hi, i was implementing strstr() to see how it works. Code: #include<iostream> using namespace std; int main() { char str[] ...

  1. #1
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    strstr() question

    hi, i was implementing strstr() to see how it works.

    Code:
    #include<iostream>
    using namespace std;
    
    int main()
    {
    char str[] = "this is a test";
    char*s;
    s=strstr(str,"test");
    cout<<s<<endl;
    
    }

    i have two question .

    question 1 > what is the full form of strstr() ?

    for example, if i write strcpy ---> it means string copy.

    similarly what is the meaning of strstr() ?

    the syntaxex dont give the full form of this function. can you tell what is the literal meaning?


    question 2.


    without assigning a memory (by new keyword ) the code is running!!

    look, i have simply tested with only char *s; but no memory allocated.
    blue_gene

  2. #2
    & the hat of GPL slaying Thantos's Avatar
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    1) most likely string string
    2) Read up on pointers more. There is no need to assign memory in this example. s will get the value that is returned by strstr(). In the example it will get the address of the first t in test, or str[10]

  3. #3
    Code Goddess Prelude's Avatar
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    >what is the full form of strstr() ?
    Does it really matter? Just call it "string string" and be done with it.

    >the code is running!!
    I'm surprised:

    >#include<iostream>
    >using namespace std;
    These will give you errors in C.

    >s=strstr(str,"test");
    You didn't include <string.h> for strstr.

    >cout<<s<<endl;
    If you compile as C, the compiler will complain about this too.

    >(by new keyword )
    You mean by malloc, since you posted on the C board.

    >but no memory allocated
    Because strstr returns a pointer to a location within the string you give it as the first argument. The memory already exists, has been initialized (we hope!) and theoretically, you own it. There's no need to allocate memory.
    My best code is written with the delete key.

  4. #4
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    You didn't include <string.h> for strstr.
    hmmm, but it worked in my compiler. my compiler version

    g++ -v

    gcc version 3.2.2 20030222 (Red Hat Linux 3.2.2-5)
    blue_gene

  5. #5
    Code Goddess Prelude's Avatar
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    >but it worked in my compiler
    Do you want a cookie? It works on my compiler too (with a warning), but that doesn't make it right.
    My best code is written with the delete key.

  6. #6
    lost in the stack...
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    cout<<s<<endl;
    Doesn't the above part of the code make it C++, and not plain old C?
    Just thought I'd point that out.

  7. #7
    Code Goddess Prelude's Avatar
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    >Doesn't the above part of the code make it C++, and not plain old C?
    Yes. It was already mentioned, but thank you anyway.
    My best code is written with the delete key.

  8. #8
    End Of Line Hammer's Avatar
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    Here's a C version of the code. Please don't post C++ code in this forum, instead, use this one.
    Code:
     #include <stdio.h>
     #include <string.h>
     
     int main(void)
     {
       char buf[] = "this is a small message";
       char *p;
       
       if ((p = strstr(buf, "small")) != NULL)
       {
     	printf ("p now points to --- %s ---\n", p);
       }
       
       return(0);
     }
    When all else fails, read the instructions.
    If you're posting code, use code tags: [code] /* insert code here */ [/code]

  9. #9
    C++ Developer XSquared's Avatar
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    >hmmm, but it worked in my compiler. my compiler version
    >g++ -v
    g++ is the GNU C++ compiler. For C, you use gcc.
    Naturally I didn't feel inspired enough to read all the links for you, since I already slaved away for long hours under a blistering sun pressing the search button after typing four whole words! - Quzah

    You. Fetch me my copy of the Wall Street Journal. You two, fight to the death - Stewie

  10. #10
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    sorry for posting C++ code.

    my demo test was bad. i thought it will return only the matched string. but it is returning the whole string after the matched string.

    anyway,

    from hammers code can i simply extract "small" to be printed ?



    another code

    Code:
     #include <stdio.h>
     #include <string.h>
    
     int main(void)
     {
       char buf[] = "this is a small message";
       char *p;
    
       if ((p = strstr(buf, "is")) != NULL)   // a littele change here
       {
            printf ("p now points to %s \n", p);
       }
    
       return(0);
     }

    output
    ./a.out

    p now points to is is a small message


    look there is double "is".....why two "is" ?
    blue_gene

  11. #11
    C++ Developer XSquared's Avatar
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    Look at the message. Now lop off the first two letters. Whaddaya get?
    Naturally I didn't feel inspired enough to read all the links for you, since I already slaved away for long hours under a blistering sun pressing the search button after typing four whole words! - Quzah

    You. Fetch me my copy of the Wall Street Journal. You two, fight to the death - Stewie

  12. #12
    Code Goddess Prelude's Avatar
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    >from hammers code can i simply extract "small" to be printed ?
    It takes a little more effort:
    Code:
    #include <stdio.h>
    #include <string.h>
    
    int main(void)
    {
      char buf[] = "this is a small message";
      char *p;
    
      if ((p = strstr(buf, "small")) != NULL)
      {
        p[ strlen ("small") ] = '\0';
        printf ("p now points to %s \n", p);
      }
    
      return(0);
    }
    If you don't want to modify the original string then you're stuck with copying the right number of characters to another buffer and then printing that one.
    My best code is written with the delete key.

  13. #13
    former member Brain Cell's Avatar
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    similarly what is the meaning of strstr() ?
    I'd say it means "String string" referring to its usage where it searchs for a string within a string.
    My Tutorials :
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