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Documented example of eina_value struct usage.
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@ -41,7 +41,8 @@ SRCS = \
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eina_model_01.c \
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eina_model_02.c \
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eina_model_03.c \
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eina_value_01.c
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eina_value_01.c \
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eina_value_02.c
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examples_PROGRAMS =
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@ -82,7 +83,8 @@ examples_PROGRAMS += \
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eina_model_02 \
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eina_model_03 \
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eina_model_04 \
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eina_value_01
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eina_value_01 \
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eina_value_02
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eina_model_04_SOURCES = \
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eina_model_04_animal.c \
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@ -0,0 +1,97 @@
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#include <Eina.h>
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static Eina_Value_Struct_Desc *V1_DESC = NULL;
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static Eina_Value_Struct_Desc *V2_DESC = NULL;
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void value_init(void)
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{
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typedef struct _My_Struct_V1 {
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int param1;
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char param2;
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} My_Struct_V1;
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static Eina_Value_Struct_Member v1_members[] = {
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// no eina_value_type as they are not constant initializers, see below.
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EINA_VALUE_STRUCT_MEMBER(NULL, My_Struct_V1, param1),
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EINA_VALUE_STRUCT_MEMBER(NULL, My_Struct_V1, param2)
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};
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v1_members[0].type = EINA_VALUE_TYPE_INT;
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v1_members[1].type = EINA_VALUE_TYPE_CHAR;
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static Eina_Value_Struct_Desc v1_desc = {
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EINA_VALUE_STRUCT_DESC_VERSION,
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NULL, // no special operations
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v1_members,
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EINA_C_ARRAY_LENGTH(v1_members),
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sizeof(My_Struct_V1)
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};
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V1_DESC = &v1_desc;
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typedef struct _My_Struct_V2 {
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int param1;
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char param2;
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int param3;
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} My_Struct_V2;
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static Eina_Value_Struct_Member v2_members[] = {
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// no eina_value_type as they are not constant initializers, see below.
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EINA_VALUE_STRUCT_MEMBER(NULL, My_Struct_V2, param1),
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EINA_VALUE_STRUCT_MEMBER(NULL, My_Struct_V2, param2),
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EINA_VALUE_STRUCT_MEMBER(NULL, My_Struct_V2, param3)
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};
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v2_members[0].type = EINA_VALUE_TYPE_INT;
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v2_members[1].type = EINA_VALUE_TYPE_CHAR;
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v2_members[2].type = EINA_VALUE_TYPE_INT;
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static Eina_Value_Struct_Desc v2_desc = {
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EINA_VALUE_STRUCT_DESC_VERSION,
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NULL, // no special operations
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v2_members,
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EINA_C_ARRAY_LENGTH(v2_members),
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sizeof(My_Struct_V2)
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};
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V2_DESC = &v2_desc;
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}
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void rand_init(Eina_Value *v)
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{
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if (v->type != EINA_VALUE_TYPE_STRUCT)
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return;
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eina_value_struct_set(v, "param1", rand());
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eina_value_struct_set(v, "param2", rand() % 256);
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eina_value_struct_set(v, "param3", rand());
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}
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void my_struct_use(Eina_Value *params)
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{
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int p1, p3;
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char p2;
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eina_value_struct_get(params, "param1", &p1);
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eina_value_struct_get(params, "param2", &p2);
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printf("param1: %d\nparam2: %c\n", p1, p2);
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if (eina_value_struct_get(params, "param3", &p3))
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printf("param3: %d\n", p3);
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}
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int main(int argc, char **argv)
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{
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Eina_Value *v1, *v2;
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eina_init();
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value_init();
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srand(time(NULL));
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v1 = eina_value_struct_new(V1_DESC);
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v2 = eina_value_struct_new(V2_DESC);
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rand_init(v1);
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my_struct_use(v1);
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rand_init(v2);
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my_struct_use(v2);
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eina_value_free(v1);
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eina_value_free(v2);
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eina_shutdown();
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}
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@ -92,6 +92,75 @@
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* @example eina_value_01.c
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*/
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/**
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* @page eina_value_example_02_page Eina_Value struct usage
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* @dontinclude eina_value_02.c
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*
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* This example will examine a hypothetical situation in which we had a
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* structure(which represented parameters) with two fields, and then need to add
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* a third field to our structure. If using structs directly we'd need to
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* rewrite every piece of code that touches the struct, by using eina value, and
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* thus having the compiler not even know the struct, we can reduce the amount
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* of changes needed and retain interoperability between the old and new format.
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*
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* Our example will start with a function that creates descriptions of both of
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* our structs for eina value usage. The first step is to create a struct and
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* describe its members:
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* @until v1_members[1]
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* @note We can't pass the types of the members to EINA_VALUE_STRUCT_MEMBER
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* macro because they are not constant initializers.
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*
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* So far it should be pretty easy to understand, we said @c My_Struct_V1 has
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* two members, one of type @c int and another of type @c char. We now create
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* the description of the actual struct, again nothing overly complex, we signal
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* which version of EINA_VALUE_STRUCT we're using, we declare no special
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* operations, our members and our size:
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* @until V1_DESC
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*
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* We now repeat the process for the second version of our struct, the only
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* difference is the addition of a third parameter of type @c int :
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* @until V2_DESC
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* @until }
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*
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* We'll now look at a function that sets the values of our structs. For
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* simplicity's sake we initialize it we random values, a real world case would
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* read these values from a file, a database or even from the network. The
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* fundamental detail here is that this function works for both V1 and V2
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* structs, this is because setting a parameter that a struct that doesn't have
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* does nothing without throwing any errors:
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* @until }
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* @note While using eina_value_struct_set() with an in-existing parameter
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* causes no error, it does return #EINA_FALSE, to notify it was not possible
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* to set the value. This could be used to determine that we're handling a V1
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* struct and take some action based on that.
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*
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* The next thing is to do is see what a function that uses the values of the
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* struct looks like. We'll again be very simplistic in our usage, we'll just
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* print the values, but a real world case, might send these values to another
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* process use them to open a network/database connection or anything else.
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* Since all versions of the struct have @c param1 and @c param2 we'll
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* unconditionally use them:
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* @until printf
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*
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* The next step is to conditionally use @c param3, which can fortunately be
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* done in the same step in which we get it's value:
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* @until }
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*
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* There we've now got functions that can both populate and use values from both
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* our structs, so now let's actually use them in our main function by creating
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* a struct of each type, initializing them and them using them:
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* @until }
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*
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* This concludes our example. For the full source code see @ref
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* eina_value_02_c.
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*/
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/**
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* @page eina_value_02_c eina_value_02.c
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* @include eina_value_02.c
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* @example eina_value_02.c
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*/
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/**
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* @addtogroup Eina_Data_Types_Group Data Types
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*
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@ -124,6 +193,7 @@
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*
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* Examples of usage of the Eina_Value API:
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* @li @ref eina_value_example_01_page
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* @li @ref eina_value_example_02_page
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*
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* @{
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*/
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