Parse complex JSON sub objects in C with YAJL

问题:

I have YAJL parsing me simple elements like given in the included example without a problem. (strings, integers, arrays, ...)

The example code can be found here: http://lloyd.github.io/yajl/yajl-2.0.1/example_2parse_config_8c-example.html

but now I have this type of JSON object:

{ "cmd":2, "properties":     [         {         "idx":40,         "val":8813.602692         },         {         "idx":41,         "val":960         },         {         "idx":42,         "val":2         },         {         "idx":48,         "val":9         }     ] 

}

I can retrieve the command with (see the definitions of used variables in the linked example):

const char * path[] = {"cmd", (const char *) 0 }; yajl_val v = yajl_tree_get(ynode, path, yajl_t_number); if (v)   *cmd = (commands)((int)YAJL_GET_INTEGER(v)); 

And I can get the reference to the properties array using:

int ar_sz; const char * path[] = {"properties", (const char *) 0 }; yajl_val v = yajl_tree_get(ynode, path, yajl_t_array); if (v)   {   ar_sz = v->u.array.len;   } 

It gives me the correct array size, but I have no clue on how to retrieve the nested elements idx and val from the array elements.

Any help is very appreciated

回答1:

By looking at the yajl_tree.h specifically the yajl_val_s structure:

{     const char * path[] = { "properties", (const char *) 0 };     yajl_val v = yajl_tree_get( node, path, yajl_t_array );     if ( v && YAJL_IS_ARRAY( v ) ) {         printf( "is array\n" );          // iterate over array elements,         // it's an array so access array.len inside yajl_val_s.union         size_t len = v->u.array.len;         int i;         for ( i = 0; i < len; ++i ) {              // get ref to one object in array at a time             yajl_val obj = v->u.array.values[ i ]; // object             // iterate over values in object: pairs of (key,value)             // u.object.len tells you number of elements             size_t nelem = obj->u.object.len;             int ii;             for ( ii = 0; ii < nelem; ++ii ) {                 // key is just char *                 const char * key = obj->u.object.keys[ ii ];     // key                 // values is an array object                 yajl_val val = obj->u.object.values[ ii ];       // val                // example: check if double,                // could do more checks or switch on value ...                if ( YAJL_IS_DOUBLE( val ) )                     printf( "%s/%f ", key, val->u.number.d );             }             printf( "\n" );         }     } else { printf( "is not array\n" ); } } 

Output should be something like:

is array idx/40.000000 val/8813.602692  idx/41.000000 val/960.000000  idx/42.000000 val/2.000000  idx/48.000000 val/9.000000  

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