writing a grep program

This is a discussion on writing a grep program within the C Programming forums, part of the General Programming Boards category; Hi, This is not a homework problem. This is a sample test problem and I wanted to know how to ...

  1. #1
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    writing a grep program

    Hi,
    This is not a homework problem. This is a sample test problem and I wanted to know how to do it. It would be great if someone can help me. The question is:

    Write a program, similar to grep, using regcomp(3C) and regexec(3C) to search for a regular expression pattern in standard input. Program synopsis:

    ./p1 pattern

    Simple search for regular expression pattern in standard input.

    Exit status:

    0 One or more matches were found
    1 No matches were found
    2 Syntax errors or inaccessible files (even if matches were found)

    Use regcomp flags: REG_NEWLINE | REG_NOSUB
    Use a function in the form:

    void regex_search( regex_t *preg, FILE *fp)

    to perform the search. This function will be invoked from the main program as:
    regex_t reg;
    ...
    regex_search( &reg, stdin);


    I did not undertsnd how to do it as I am not very familiar with C. I am from an IC design background. It would be a great help for my exam preparations, if somebody can help me with this.

    Thankyou very much.
    -Cnovice

  2. #2
    and the hat of wrongness Salem's Avatar
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    Use fgets() to read each line from a file.
    Apply your regex matcher to each line.

    Lather, rinse and repeat until end of file.

  3. #3
    Frequently Quite Prolix dwks's Avatar
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    Use fgets() to read each line from a file.
    In C++? Really? I thought you were supposed to use getline or something.
    dwk

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    fgets() is part of the c++ language isn't it?

  5. #5
    Frequently Quite Prolix dwks's Avatar
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    Yeah, but it's like using printf().
    dwk

    Seek and ye shall find. quaere et invenies.

    "Simplicity does not precede complexity, but follows it." -- Alan Perlis
    "Testing can only prove the presence of bugs, not their absence." -- Edsger Dijkstra
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    and printf() is also part of the c++ language, although admittedly not commonly used in c++ programs

  7. #7
    Frequently Quite Prolix dwks's Avatar
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    Okay, then, it's like using malloc(). Yeah, you can use it, but there are alternatives. (new, in the case of malloc.)

    (You're not supposed to use malloc() in C++ programs because it just allocates memory, it doesn't call constructors.)
    dwk

    Seek and ye shall find. quaere et invenies.

    "Simplicity does not precede complexity, but follows it." -- Alan Perlis
    "Testing can only prove the presence of bugs, not their absence." -- Edsger Dijkstra
    "The only real mistake is the one from which we learn nothing." -- John Powell


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  8. #8
    and the hat of wrongness Salem's Avatar
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    > I did not undertsnd how to do it as I am not very familiar with C.
    I didn't read the board, I read this.
    Hence the 'C' answer.

    Moved to the 'C' board.

  9. #9
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    Quote Originally Posted by dwks
    Okay, then, it's like using malloc(). Yeah, you can use it, but there are alternatives. (new, in the case of malloc.)

    (You're not supposed to use malloc() in C++ programs because it just allocates memory, it doesn't call constructors.)
    but sometimes that's all you want anyway, especially when allocating arrays of PODs or structures that contain nothing but POD data objects. However, for consistency, I agree with you that malloc() and new should not be used in the same breath (program).

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