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5 Copyright (c) 2020 AT&T Intellectual Property.
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15 WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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18 ==================================================================================
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 &fig_cen(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).
69 "lodge_name": "Water Buffalo Lodge 714",
71 "grand_poobah": "Larry K. Slate",
72 "attendance": [ 23, 14, 41, 38, 24 ],
74 "street": "16801 Stonway Lane",
80 "owner": "Stonegate Properties",
83 "contact:" "Kyle Limestone"
87 &export_fig( jblob_fig )
88 &fig_cen(Sample json with a root and two blobs.)
91 &ifroom( 3i : blob_ex.ca )
94 Upon creation of the Jhash object, the &ital(root) fields, &cw(lodge_name,) &cw(member_count,) and
95 &cw(grand_poobah) are immediately available.
96 The fields in the &ital(sub-blobs) are available only when the correct blob is selected.
97 The code sample in figure &fig_blob_sample illustrates how a &ital(sub-blob) is selected.
100 jh->Set_blob( (char *) "address" ); // select address
101 jh->Unset_blob(); // return to root
102 jh->Set_blob( (char *) "lease_info" ); // select the lease blob
105 &export_fig( fig_blob_sample )
106 &fig_cen(Blob selection example.)
109 Currently, the selected blob must be unset in order to select a blob at the root
110 level; unset always sets the root blob.
111 Attempting to use the &cw(Set_blob) function will attempt to select the named blob
112 from the current blob, and not the root.
114 &h2(Simple Value Extraction)
115 Simple values are the expected data types &ital(string, value,) and &ital(boolean.)
116 This lightweight json parser treats all values as floating point numbers and does not
117 attempt to maintain a separate integer type.
118 A fourth type, &ital(null,) is supported to allow the user to expressly check for
119 a field which is defined but has no value; as opposed to a field that was completely
120 missing from the data.
121 The following are the prototypes for the functions which allow values to be extracted:
125 std::string String( const char* name );
126 float Value( const char* name );
127 bool Bool( const char* name );
131 Each of these functions returns the value associated with the field with the given &ital(name.)
132 If the value is missing, the following default values are returned:
136 &beg_dlist( 1i Helvetica-bold : : 15,80 )
137 &di(String:) An empty string (.e.g "").
138 &di(Value:) Zero (e.g 0.0)
144 If the user needs to disambiguate between a missing value and the default value either the
145 &cw(Missing) or &cw(Exists) function should be used first.
147 &h2(Testing For Existing and Missing Fields)
148 Two functions allow the developer to determine whether or not a field is included in the
150 Both of these functions work on the current &ital(blob,) therefore it is important to ensure
151 that the correct blob is selected before using either of these functions.
152 The prototypes for the &cw(Exists) and &cw(Missing) functions are below:
155 bool Exists( const char* name );
156 bool Is_missing( const char* name );
159 The &cw(Exists) function returns &ital(true) if the field name exists in the json and &ital(false) otherwise.
160 Conversely, the &cw(Missing) function returns &ital(true) when the field name does not exist in the json.
163 &h2(Testing Field Type)
164 The &cw(Exists) and &cw(Missing) functions might not be enough for the user code to validate
165 the data that it has.
166 To assist with this, several functions allow direct type testing on a field in the current
168 The following are the prototypes for these functions:
171 bool Is_bool( const char* name );
172 bool Is_null( const char* name );
173 bool Is_string( const char* name );
174 bool Is_value( const char* name );
178 Each of these functions return &ital(true) if the field with the given name is of the type
183 Arrays are supported in the same manner as simple field values with the addition of the need
184 to supply an array index when fetching values from the object.
185 In addition, there is a &ital(length) function which can be used to determine the number
186 of elements in the named array.
187 The prototypes for the array based functions are below:
190 int Array_len( const char* name );
192 bool Is_bool_ele( const char* name, int eidx );
193 bool Is_null_ele( const char* name, int eidx );
194 bool Is_string_ele( const char* name, int eidx );
195 bool Is_value_ele( const char* name, int eidx );
197 bool Bool_ele( const char* name, int eidx );
198 std::string String_ele( const char* name, int eidx );
199 float Value_ele( const char* name, int eidx );
203 For each of these functions the &cw(eidx) is the zero based element index which is to
204 be tested or selected.
207 An array containing blobs, rather than simple field value pairs, the blob must
208 be selected prior to using it, just as a sub-blob needed to be selected.
209 The &cw(Set_blob_ele) function is used to do this and has the following prototype:
212 bool Set_blob_ele( const char* name, int eidx );
216 As with selecting a sub-blob, an unset must be performed before selecting the next blob.
217 Figure &array_blob_code_fig illustrates how these functions can be used to read and print
218 values from the json in figure &array_blob_json_fig.
224 { "name": "Fred Flinstone", "member_num": 42 },
225 { "name": "Barney Rubble", "member_num": 48 },
226 { "name": "Larry K Slate", "member_num": 22 },
227 { "name": "Kyle Limestone", "member_num": 49 }
230 &export_fig(array_blob_code_fig)
231 &fig_cen(Json array containing blobs.)
241 len = jh->Array_len( (char *) "members" );
242 for( i = 0; i < len; i++ ) {
243 jh->Set_blob_ele( (char *) "members", i ); // select blob
245 mname = jh->String( (char *) "name" ); // read values
246 mnum = jh->Value( (char *) "member_num" );
247 fprintf( stdout, "%s is member %d\n", mname.c_str(), (int) mnum );
249 jh->Unset_blob(); // back to root
252 &export_fig(array_blob_json_fig )
253 &fig_cen(Code to process the array of blobs.)