OSSP val - Value Access Library "VAL_MAXNAME", "VAL_TYPE_VAL", "VAL_TYPE_PTR", "VAL_TYPE_CHAR", "VAL_TYPE_SHORT", "VAL_TYPE_INT", "VAL_TYPE_LONG", "VAL_TYPE_FLOAT", "VAL_TYPE_DOUBLE" "VAL_OK", "VAL_ERR_ARG", "VAL_ERR_USE", "VAL_ERR_MEM", "VAL_ERR_HSH", "VAL_ERR_INT", "VAL_ERR_SYS". "val_t", "val_cb_t", "val_rc_t". "val_create", "val_destroy", "val_reg", "val_unreg", "val_query", "val_set", "val_get", "val_vset", "val_vget", "val_apply". OSSP val is a flexible name to value mapping library for ISO-C variables. It allows one to access ISO-C variables through name strings, although the ISO-C language does neither provide such a dedicated facility nor an evaluation construct (which could be used to implement such a facility easily). In general, this is used for accessing ISO-C variables without having to know the actual symbol/address. The typical use cases are in combination with flexible configuration parsing and supporting loosly-coupled DSO-based module architectures. Whenever the APIs calls for a name, it supports structured names where elements are separated by a dot. It is assumed that the leading elements are references to other "val_t" structures and only the very last element is a reference to an actual variable. The maximum length of a variable name. For structured variables this includes the concatenation of all elements within a path and their separating dots. Type of value when registering a variable using val_reg() or querying for the type using val_query(). Most are self-explanatory because directly correspond to the basic C data types. "VAL_TYPE_VAL" is used to mount a "val_t" structure into an existing "val_t" structure to support structured names (see example section for details). The following particular types exist: "VAL_TYPE_VAL", "VAL_TYPE_PTR", "VAL_TYPE_CHAR", "VAL_TYPE_SHORT", "VAL_TYPE_INT", "VAL_TYPE_LONG", "VAL_TYPE_FLOAT", "VAL_TYPE_DOUBLE" Return codes (of type "val_rc_t") for every API function. Signals success ("VAL_OK"), invalid argument passed to function, bad usage of a function, memory usage reached "VAL_MAXNAME" limit, error in internal hash function to be examined through "errno", internal error in storage as result from structure corruption, or system errors including out of memory to be examined through "errno". The following particular return codes exist: "VAL_OK", "VAL_ERR_ARG", "VAL_ERR_USE", "VAL_ERR_MEM", "VAL_ERR_HSH", "VAL_ERR_INT", "VAL_ERR_SYS". Opaque handle data type created by val_create() and passed to all other functions to reference the the same group of values. Function data type for the callback to be used with var_apply(). Data type returned by every function. See API CONSTANTS "VAL_OK" and "VAL_ERR_"ID. Creates a new value structure and updates the given pointer to reference it. Destroys a val structure. Registers a value under name of type type in val. An optional description or "NULL" can be passed through desc which can be queried through val_query() and is also passed to the callback of val_apply(). The value that belongs to the given name is expected to be found at storage. Passing "NULL" as storage will create an internal data storage in val so it can only be access through val_get(), val_set() or after the actual storage address was queried using val_query(). Unregisters the value under name in val. Queries a value name in val and returns its type, description and storage address. All of ptype, pdesc and pstorage are optional and "NULL" can be passed in if this information is not needed. Passing "NULL" to all query result pointers just checks for existence of the value name in val. Sets the value name in val to the data passed in as the variable argument (expected to be of the type specified at val_reg() time). Unless the actual storage address was queried using val_query() this operation is mandatory for internally stored data. If external storage is used, not the value but a pointer to it is stored in the library, so the value is allowed to be be modified without notice to the library. Gets the value name in val and stores it whereever the passed variable argument points to. The storage location is expected to be of the type specified at val_reg() time. Exactly like val_set() but uses a "va_list". Exactly like val_get() but uses a "va_list". Iterates over all values in val, starting with name, which can be either a data storage or val_t reference, down to a given recursion depth. If name is set to the empty string the search starts immediately at val. For every value, the callback cb() is executed. The callback has to be a function with the following prototype: val_rc_t cb(void *ctx, const char *name, int type, const char *desc, void *storage); The ctx is the passed-through context ctx of val_apply(). The name is the structured name relative to the val passed to val_apply(), type signals the type of value storage points to and desc is the text which was optionally passed to val_reg(). OSSP var (Variable Expansion) A few simple examples on how to use OSSP val are following. For easier reading all error checks are omitted. In a production program you have to check every val_xxx() call against "VAL_OK", of course.

Simple Internal Value
Source: #include <stdio.h> #include "val.h" int main(void) { val_rc_t rc; val_t *v; int tmp; val_create(&v); val_reg(v, "foo", VAL_TYPE_INT, "foo variable", NULL); val_set(v, "foo", 123); val_get(v, "foo", &tmp); printf("foo=%d\n", tmp); val_destroy(v); return 0; } Output: foo=123

Simple External Value
Source: #include <stdio.h> #include "val.h" int main(void) { val_rc_t rc; val_t *v; int foo; int tmp; val_create(&v); val_reg(v, "foo", VAL_TYPE_INT, "foo variable", (void *)&foo); foo = 123; val_get(v, "foo", &tmp); printf("1. foo=%d tmp=%d\n", foo, tmp); val_set(v, "foo", 456); val_get(v, "foo", &tmp); printf("2. foo=%d tmp=%d\n", foo, tmp); example = 789; val_get(v, "foo", &tmp); printf("3. foo=%d tmp=%d\n", foo, tmp); val_destroy(v); return 0; } Output: 1. foo=123 tmp=123 2. foo=456 tmp=456 3. foo=789 tmp=789

Structured Internal Values
Source: #include <stdio.h> #include "val.h" int main(void) { val_rc_t rc; val_t *v1, *v2; int tmp; val_create(&v1); val_create(&v2); val_reg(v1, "bar", VAL_TYPE_VAL, "v2", (void *)&v2); val_reg(v1, "bar.foo", VAL_TYPE_INT, "foo variable", NULL); val_set(v2, "foo", 123); val_get(v2, "foo", &tmp); printf("1. foo=%d\n", tmp); val_get(v1, "bar.foo", &tmp); printf("2. bar.foo=%d\n", tmp); val_set(v1, "bar.foo", 456); val_get(v2, "foo", &tmp); printf("3. foo=%d\n", tmp); val_destroy(v2); val_destroy(v1); return 0; } Output: 1. foo=123 2. bar.foo=123 3. foo=456 OSSP val was invented in January 2002 by Thomas Lotterer and Ralf S. Engelschall for use with the OSSP lmtp2nntp project. Thomas Lotterer <thomas.lotterer@cw.com> Ralf S. Engelschall <rse@engelschall.com>