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23 This imbed file contains the portion of the document that describes the
24 json support that is provided by the framework.
29 The C++ xAPP framework provides a very lightweight json parser and data
31 Briefly, a json hash (Jhash) can be established by creating an instance of
32 the Jhash object with a string of valid json.
33 The resulting object's functions can then be used to read values from the
37 &h2(Creating The Jhash Object)
38 The Jhash object is created simply by passing a json string to the constructor.
42 #include <ricxfcpp/Jhash>
44 std::string jstring = "{ \"tag\": \"Hello World\" }";
47 jh = new Jhash( jstring.c_str() );
49 &figure(The creation of the Jhash object.)
53 Once the Jhash object has been created any of the methods described in the following
54 paragraphs can be used to retrieve the data:
57 Json objects can be nested, and the nesting is supported by this representation.
58 The approach taken by Jhash is a "directory view" approach, where the "current directory,"
59 or current &ital(blob,) limits the scope of visible fields.
62 As an example, the json contained in figure jblob_fig, contains a "root" blob and
63 two &ital(sub-blobs) (address and lease_info).
67 "lodge_name": "Water Buffalo Lodge 714",
69 "grand_poobah": "Larry K. Slate",
70 "attendance": [ 23, 14, 41, 38, 24 ],
72 "street": "16801 Stonway Lane",
78 "owner": "Stonegate Properties",
81 "contact:" "Kyle Limestone"
87 &set_fref(jblob_fig:&_fig)
88 &figure(Sample json with a root and too blobs.)
91 Upon creation of the Jhash object, the &ital(root) fields, &cw(lodge_name,) &cw(member_count,) and
92 &cw(grand_poobah) are immediately available.
93 The fields in the &ital(sub-blobs) are avalable only when the correct blob is selected.
94 The code sample in figure &fig_blob_sample illustrates how a &ital(sub-blob) is selected.
97 jh->Set_blob( (char *) "address" ); // select address
98 jh->Unset_blob(); // return to root
99 jh->Set_blob( (char *) "lease_info" ); // slect the lease blob
103 &set_fref(fig_blob_sample:&_fig)
104 &figure(Blob selection example.)
107 Currently, the selected blob must be unset in order to select a blob at the root
108 level; unset always sets the root blob.
109 Attempting to use the &cw(Set_blob) function will attempt to select the named blob
110 from the current blob, and not the root.
112 &h2(Simple Value Extraction)
113 Simple values are the expected data types &ital(string, value,) and &ital(boolean.)
114 This lightweight json parser treats all values as floating point numbers and does not
115 attempt to maintain a separate integer type.
116 A fourth type, &ital(null,) is supported to allow the user to expressly check for
117 a field which is defined but has no value; as opposed to a field that was completely
118 missing from the data.
119 The following are the prototypes for the functions which allow values to be extracted:
123 std::string String( const char* name );
124 float Value( const char* name );
125 bool Bool( const char* name );
129 Each of these funcitons returns the value associated with the field with the given &ital(name.)
130 If the value is missing, the following default values are returned:
134 &beg_dlist( 1i Helvetica-bold : : 15,80 )
135 &di(String:) An empty string (.e.g "").
136 &di(Value:) Zero (e.g 0.0)
142 If the user needs to disambiguate between a missing value and the default value either the
143 &cw(Missing) or &cw(Exists) function should be used first.
145 &h2(Testing For Existing and Missing Fields)
146 Two functions allow the developer to determine whether or not a field is included in the
148 Both of these functions work on the current &ital(blob,) therefore it is important to ensure
149 that the correct blob is selected before using either of these funcitons.
150 The prototpyes for the &cw(Exists) and &cw(Missing) functions are below:
153 bool Exists( const char* name );
154 bool Is_missing( const char* name );
157 The &cw(Exists) function returns &ital(true) if the field name exists in the json and &ital(false) otherwise.
158 Conversly, the &cw(Missing) funciton returns &ital(true) when the field name does not exist in the json.
161 &h2(Testing Field Type)
162 The &cw(Exists) and &cw(Missing) functions might not be enough for the user code to validate
163 the data that it has.
164 To assist with this, several functions allow direct type testing on a field in the current
166 The following are the prototypes for these functions:
169 bool Is_bool( const char* name );
170 bool Is_null( const char* name );
171 bool Is_string( const char* name );
172 bool Is_value( const char* name );
176 Each of these funcitons return &ital(true) if the field with the given name is of the type
181 Arrays are supported in the same manner as simple field values with the addition of the need
182 to supply an array index when fetching values from the object.
183 In addition, there is a &ital(length) function which can be used to determine the number
184 of elements in the named array.
185 The prototypes for the array based functions are below:
188 int Array_len( const char* name );
190 bool Is_bool_ele( const char* name, int eidx );
191 bool Is_null_ele( const char* name, int eidx );
192 bool Is_string_ele( const char* name, int eidx );
193 bool Is_value_ele( const char* name, int eidx );
195 bool Bool_ele( const char* name, int eidx );
196 std::string String_ele( const char* name, int eidx );
197 float Value_ele( const char* name, int eidx );
201 For each of these functions the &cw(eidx) is the zero based element index which is to
202 be tested or selected.
205 An array containing blobs, rather than simiple field value pairs, the blob must
206 be selected prior to using it, just as a sub-blob needed to be selected.
207 The &cw(Set_blob_ele) function is used to do this and has the following prototype:
210 bool Set_blob_ele( const char* name, int eidx );
214 As with selecting a sub-blob, an unset must be preformed before selecting the next blob.
215 Figure &array_blob_code_fig illustrates how these functions can be used to read and print
216 values from the json in figure &array_blob_json_fig.
222 { "name": "Fred Flinstone", "member_num": 42 },
223 { "name": "Barney Rubble", "member_num": 48 },
224 { "name": "Larry K Slate", "member_num": 22 },
225 { "name": "Kyle Limestone", "member_num": 49 }
229 &set_fref(array_blob_code_fig:&_fig)
230 &figure(Json array containing blobs.)
240 len = jh->Array_len( (char *) "members" );
241 for( i = 0; i < len; i++ ) {
242 jh->Set_blob_ele( (char *) "members", i ); // select blob
244 mname = jh->String( (char *) "name" ); // read values
245 mnum = jh->Value( (char *) "member_num" );
246 fprintf( stdout, "%s is member %d\n", mname.c_str(), (int) mnum );
248 jh->Unset_blob(); // back to root
252 &set_fref(array_blob_json_fig:&_fig)
253 &figure(Code to process the array of blobs.)