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POC strcpy() - evil?
 

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    <p>Some people seem to think that C's <code>strcpy()</code> function is bad or evil. While I admit that it's usually better to use <code>strncpy()</code> in order to avoid buffer overflows, the following (an implementation of the <code>strdup()</code> function for those not lucky enough to have it) safely uses <code>strcpy()</code> and should <em>never</em> overflow:</p> <pre><code>char *strdup(const char *s1) { char *s2 = malloc(strlen(s1)+1); if(s2 == NULL) { return NULL; } strcpy(s2, s1); return s2; } </code></pre> <p><code>*s2</code> is guaranteed to have enough space to store <code>*s1</code>, and using <code>strcpy()</code> saves us from having to store the <code>strlen()</code> result in another function to use later as the unnecessary (in this case) length parameter to <code>strncpy()</code>. Yet some people write this function with <code>strncpy()</code>, or even <code>memcpy()</code>, which both require a length parameter. I would like to know what people think about this. If you think <code>strcpy()</code> is safe in certain situations, say so. If you have a good reason not to use <code>strcpy()</code> in this situation, please give it - I'd like to know why it might be better to use <code>strncpy()</code> or <code>memcpy()</code> in situations like this. If you think <code>strcpy()</code> is okay, but not here, please explain.</p> <p>Basically, I just want to know why some people use <code>memcpy()</code> when others use <code>strcpy()</code> and still others use plain <code>strncpy()</code>. Is there any logic to preferring one over the three (disregarding the buffer checks of the first two)?</p>
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    1. USChris Lutz
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    1. COIn multi-threaded environment it's rarely reasonable for every library function to handle locking itself.
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    2. COSince strlen may segfault, or return an unreasonably large value on an improperly terminated s1, your strdup is not safe.
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      1. USkmarsh
    3. COIf 'malloc' changes 's1', then there is no guarantee that the buffer will be large enough when you later get around to copying into it with 'strcpy'. Suppose 's1' is a pointer to a string maintained internally by the memory management system -- maybe the last time 'malloc' was called.
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      1. USDavid Schwartz
 

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