Avoiding Buffer Overflows

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  1. #1
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    Avoiding Buffer Overflows

    How can one avoid buffer overflows when wanting to format strings or convert numbers to strings? Is there any equivalent functions to for ex. itoa() or sprintf(), where a maximum buffer length can be sent or a required length can be retained? Or is the only way of achieving this by writing your own functions?

    Please note that simply allocating a very large buffer is not the solution I am looking for.
    Thanks in advance
    Last edited by Aidman; 01-03-2004 at 10:31 AM.
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    and the hat of wrongness Salem's Avatar
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    Are you asking for a C answer (since you mention sprintf), or a C++ answer since you posted on the C++ forum?

    The new C99 standard introduces things like snprintf() to limit the amount of data which is copied into a buffer.
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
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    Code Goddess Prelude's Avatar
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    >How can one avoid buffer overflows when wanting to format strings or convert numbers to strings?
    One would use std::string and std::stringstream.
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    Thanks for the quick replies, no it doesn't really matter if it's a C or C++ answer.

    Is there was any function able to give the required buffer size for a number-to-string conversions?
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    Here's the specification for VC++2003:
    Code:
    #include <stdio.h>
    int _snprintf(
       char *buffer,
       size_t count,
       const char *format [,
       argument] ...
    );
    In your compiler, it might be different. Here's an example:
    Code:
    int num = 3434;
    char str[3];
    _snprintf(str, sizeof(str), "%d", num);

  6. #6
    and the hat of wrongness Salem's Avatar
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    In the absense of C99, or some implementation specific version of snprintf(), you have to do some things yourself

    > the required buffer size for a number-to-string conversions?
    For integral types, its determined by
    numchars = sizeof_type_in_bits / log2(10)

    sizeof_type_in_bits = sizeof(type) * CHAR_BIT
    log2(10) is approx 3.32, so for an easy life, use 3

    And don't forget to allow for the \0 at the end
    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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