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POSacrificing expression of intent for memory management
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copied!<p>I'm pretty new at C programming, and this type of thing keeps popping up. As a simple example, suppose I have a <code>struct http_header</code> with some <code>char</code> pointers:</p> <pre><code>struct http_header { char* name; char* value; }; </code></pre> <p>I want to fill an <code>http_header</code> where <code>value</code> is the string representation of an int. I "feel" like, semantically, I should be able to write a function that takes in an empty header pointer, a name string, and an <code>int</code> and fills out the header appropriately. </p> <pre><code>void fill_header(struct http_header *h, char* name, int value) { h->name = name; char *value_str = malloc(100); sprintf(value_str, "%d", value); h->value = value_str; } int main(int argc, const char * argv[]) { struct http_header h; char *name = "Header Name"; int val = 42; fill_header(&h, name, val); ... free(h.value); } </code></pre> <p>Here, the calling code reads exactly as my intent, but in this case I'm creating the <code>value</code> string dynamically, which means I'd have to free it later. That doesn't smell right to me; it seems like the caller then knows too much about the implementation of <code>fill_header</code>. And in actual implementations it may not be so easy to know what to free: consider filling an array of <code>http_header</code>s where only one of them needed to have its value <code>malloc</code>ed.</p> <p>To get around this, I'd have to create the string beforehand:</p> <pre><code>void fill_header2(struct http_header *h, char* name, char *value_str) { h->name = name; h->value = value_str; } int main(int argc, const char * argv[]) { struct http_header h; char *name = "Header Name"; int value = 42; char value_str[100]; sprintf(value_str, "%d", value); fill_header2(&h, name, value_str); } </code></pre> <p>As this pattern continues down the chain of structures with pointers to other structures, I end up doing so much work in top level functions the lower level ones seem hardly worth it. Furthermore, I've essentially sacrificed the "fill a header with an <code>int</code>" idea which I set out to write in the first place. I'm I missing something here? Is there some pattern or design choice that will make my life easier <em>and</em> keep my function calls expressing my intent?</p> <p>P.S. Thanks to all at Stackoverfow for being the best professor I've ever had. </p>

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