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| author | Laurent Bercot <ska-skaware@skarnet.org> | 2014-09-18 18:55:44 +0000 |
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| committer | Laurent Bercot <ska-skaware@skarnet.org> | 2014-09-18 18:55:44 +0000 |
| commit | 3534b428629be185e096be99e3bd5fdfe32d5544 (patch) | |
| tree | 210ef3198ed66bc7f7b7bf6a85e4579f455e5a36 /doc/libstddjb/stralloc.html | |
| download | skalibs-3534b428629be185e096be99e3bd5fdfe32d5544.tar.xz | |
initial commit with rc for skalibs-2.0.0.0
Diffstat (limited to 'doc/libstddjb/stralloc.html')
| -rw-r--r-- | doc/libstddjb/stralloc.html | 118 |
1 files changed, 118 insertions, 0 deletions
diff --git a/doc/libstddjb/stralloc.html b/doc/libstddjb/stralloc.html new file mode 100644 index 0000000..a5a1c7e --- /dev/null +++ b/doc/libstddjb/stralloc.html @@ -0,0 +1,118 @@ +<html> + <head> + <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /> + <meta http-equiv="Content-Language" content="en" /> + <title>skalibs: the stralloc library interface</title> + <meta name="Description" content="skalibs: the stralloc library interface" /> + <meta name="Keywords" content="skalibs c unix stralloc library libstddjb" /> + <!-- <link rel="stylesheet" type="text/css" href="http://skarnet.org/default.css" /> --> + </head> +<body> + +<p> +<a href="index.html">libstddjb</a><br /> +<a href="../libskarnet.html">libskarnet</a><br /> +<a href="../index.html">skalibs</a><br /> +<a href="http://skarnet.org/software/">Software</a><br /> +<a href="http://skarnet.org/">skarnet.org</a> +</p> + +<h1> The <tt>stralloc</tt> library interface </h1> + +<p> + The following functions are declared in the <tt>skalibs/stralloc.h</tt> header, +and implemented in the <tt>libskarnet.a</tt> or <tt>libskarnet.so</tt> library. +</p> + +<h2> General information </h2> + +<p> + <tt>stralloc</tt> is the preferred skalibs way of storing objects into +heap memory. It focuses on strings of <em>char</em>, which is the generic +way to handle any object. For easy structure manipulation, the +<a href="genalloc.html">genalloc</a> +series of functions can be used; those functions are mostly macros wrapping +calls to their stralloc counterparts. +</p> + +<p> + A stralloc is a structure containing the following fields: +</p> + +<ul> + <li> <em>s</em>: a pointer to a zone of heap memory. The stralloc +functions internally manipulate those via the +<a href="alloc.html">alloc</a> series of functions. It is recommended +to never modify that field manually. </li> + <li> <em>len</em>: the <strong>used</strong> length of the +allocated zone. It is the only field that the user can modify +directly. </li> + <li> <em>a</em>: the number of allocated bytes. The user should never +have to access that field, because the memory allocation management +should be entirely transparent. <em>len</em> cannot exceed <em>a</em>: +if an operation needs a bigger <em>len</em>, it will automatically +reallocate as needed. </li> +</ul> + +<p> + The benefits of using stralloc are as follows: +</p> + +<ul> + <li> Memory allocation is performed on-demand and automatically, with +a suitable size. Heuristics are used to accommodate constantly growing +strings while minimizing the amount of needed reallocations. </li> + <li> If every heap-allocated object is represented by a stralloc, then +it is very easy to identify what pointer is in the heap. When you stop +using a pointer <em>p</em>, should you free it ? Sometimes it's not +easy to find out. When you stop using a stralloc <em>sa</em>, you +<em>know</em> you must call <tt>stralloc_free(&sa)</tt>. Store +your strong references as strallocs and weak references as simple +pointers, and never free simple pointers. This policy allows me to +boast that <em>no skarnet.org software has ever leaked memory</em>. </li> + <li> Repeated for emphasis: +<strong> the golden rule for programming with strallocs is +<em>every pointer to the heap must be owned by a stralloc</em>. </strong> +Every pointer you handle yourself either does not point to the heap, +or is weak. That sometimes implies unusual programming practices, such +as having storage separated from structure, but it's hands down the +easiest way to keep control of your heap in complex situations. </li> +<li> The indirection layer makes weak references immune to +reallocation troubles. The <em>s</em> field may change when a +reallocation happens, but the stralloc structure's address never +changes. </li> +</ul> + +<p> + A stralloc can be declared anywhere: static/global data, stack or heap. (Of course, +as a general rule, you should favor the stack whenever possible.) +A stralloc should be initialized to STRALLOC_ZERO before its first use. +</p> + +<h2> Functions </h2> + +<p> +<code> int stralloc_catb (stralloc *sa, char const *s, unsigned int len) </code> <br /> +Appends the <em>len</em> bytes pointed to by <em>s</em> to the end of the +memory zone handled by *<em>sa</em>, automatically allocating more memory +if needed. Returns 1 if it succeeds, and 0 if it fails. +</p> + +<p> +<code> void stralloc_free (stralloc *sa) </code> <br /> +Frees <em>*sa</em>, i.e. calls <a href="alloc.html">alloc_free</a> +on <em>sa</em>→s then zeroes the structure. *<em>sa</em> is +then reusable. However, it is not good practice to call this function +if you're going to reuse *<em>sa</em> soon: it takes time and causes +memory fragmentation. Just setting <em>sa</em>→len to 0 allows +you to instantly reuse the allocated block of memory. +</p> + +<p> + The above are the most important and fundamental functions of +<tt>skalibs/stralloc.h</tt>. Other functions can be found in this header and +their prototypes are self-explaining. +</p> + +</body> +</html> |