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    <p>I personally am of the mindset that if the code can be proven to be valid—and done so quickly—it is perfectly acceptable. That is, if the code is simple and thus obviously correct, then it is fine.</p> <p>However, your assumption seems to be that while your function is executing, no other thread will modify the string pointed to by <code>s1</code>. What happens if this function is interrupted after successful memory allocation (and thus the call to <code>strlen</code>), the string grows, and <strong>bam</strong> you have a buffer overflow condition since <code>strcpy</code> copies to the NULL byte.</p> <p>The following might be better:</p> <pre><code>char * strdup(const char *s1) { int s1_len = strlen(s1); char *s2 = malloc(s1_len+1); if(s2 == NULL) { return NULL; } strncpy(s2, s1, s1_len); return s2; } </code></pre> <p>Now, the string can grow through no fault of your own and you're safe. The result will not be a dup, but it won't be any crazy overflows, either.</p> <p>The probability of the code you provided <em>actually</em> being a bug is pretty low (pretty close to non-existent, if not non-existent, if you are working in an environment that has no support for threading whatsoever). It's just something to think about.</p> <p><strong>ETA</strong>: Here is a slightly better implementation:</p> <pre><code>char * strdup(const char *s1, int *retnum) { int s1_len = strlen(s1); char *s2 = malloc(s1_len+1); if(s2 == NULL) { return NULL; } strncpy(s2, s1, s1_len); retnum = s1_len; return s2; } </code></pre> <p>There the number of characters is being returned. You can also:</p> <pre><code>char * strdup(const char *s1) { int s1_len = strlen(s1); char *s2 = malloc(s1_len+1); if(s2 == NULL) { return NULL; } strncpy(s2, s1, s1_len); s2[s1_len+1] = '\0'; return s2; } </code></pre> <p>Which will terminate it with a <code>NUL</code> byte. Either way is better than the one that I quickly put together originally.</p>
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    1. POC strcpy() - evil?
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    1. USMichael Trausch
    1. USMichael Trausch
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    1. CONot having worked with threads, I didn't think about this, but I'm glad to know there is a rational reason for this. How often do functions in one thread modify variables while other threads are working with them in threaded programs? Or is that a stupid question?
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      1. USChris Lutz
    2. COYou shouldn't be accessing any buffer that other threads modify without locking it first. Using strncpy does not make your function thread safe.
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      1. USSedat Kapanoglu
    3. CO'What happens if this function is interrupted after successful memory allocation (and thus the call to strlen), the string grows, and bam you have a buffer overflow condition since strcpy copies to the NULL byte.' well...
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      1. USJohannes Schaub - litb
 

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