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Update 12_2_Accessing_Bitcoind_with_C.md

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Shannon Appelcline 2017-06-16 12:22:08 -07:00 committed by GitHub
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12_2_Accessing_Bitcoind_with_C.md
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@ -120,18 +120,8 @@ In order to you an RPC method in `bitcoinrpc`, you must initialize a variable of
bitcoinrpc_method_t *getmininginfo = NULL;
getmininginfo = bitcoinrpc_method_init(BITCOINRPC_METHOD_GETMININGINFO);
```
You must next input the parameters for your methods, which is done by creating a JSON array, then (if necessary) filling it. This is done with the `jansson` library; see the [jansson Reference](http://jansson.readthedocs.io/en/2.8/apiref.html) for more information on its specific function calls.
Usually you would set parameters here, but in this get, `getmininginfo` requires no parameters, so we can skip that.
In this case, we just input an empty array, because we're not sending any arguments to `getmininginfo`. We'll have some increasingly complex examples of parameter submission later on.
```
json_t *params = NULL;
params = json_array();
```
The parameters are input to the method as follows. After inputting the parameters into the method, they can be neatly cleared away.
```
bitcoinrpc_method_set_params(getmininginfo, params);
json_decref(params);
```
Two more objects are required, a "response object" and an "error object". They're created via standard `bitcoinrpc` function calls:
```
bitcoinrpc_resp_t *btcresponse = NULL;
@ -143,4 +133,40 @@ And now you can put it all together to make a `getmininginfo` RPC call:
```
bitcoinrpc_call (rpc_client, getmininginfo, btcresponse, &btcerror);
```
[[AND, I JUST GET LITERALLY INDECIPHERABLE ERROR MESSAGES AT THIS POINT, AND THE SAMPLE CODE DOESN'T WORK EITHER. I'M NOT SURE IF THIS LIBRARY STILL WORKS.]]
### Output Your Response
Retrieve the output of your call with `bitcoinrpc_resp_get`.
```
json_t *jsonresponse = NULL;
jsonresponse = bitcoinrpc_resp_get (btcresponse);
```
If you want to output the complete JSON results of the RPC call, you can do so with a simple invocation of `json_dumps`, from the `jansson` library:
```
fprintf (stderr, "%s\n", json_dumps (j, JSON_INDENT(2)));
```
However since your now writing complete programs, you're probably going to want to do more subtle work, such as pulling out individual JSON values for specific usage. The [jansson Reference](https://jansson.readthedocs.io/en/2.10/apiref.html) tells how to do so.
You can then drill down to the `result` JSON object:
```
json_t *jsonresult = NULL;
jsonresult = json_object_get(jsonresponse,"result");
fprintf (stderr, "%s\n", json_dumps (jsonresult, JSON_INDENT(2)));
```
Finall, you can drill down to an individual item like `blocks`:
```
json_t *jsonblocks = NULL;
jsonresult = json_object_get(jsonresult,"blocks");
int blocks;
blocks = json_integer_value(jsonresult);
printf("Block Count: %d\n",blocks);
```
[[SUMMARY]]
[[APPENDIX 1: First Code]]
[[APPENDIX 2: First Code]]
[[clean up organizing of initialization of variables]]
[[FREE up the JSON objects]]
[[BREAK OUT TWO MORE CHAPTERS ON GETTING INFO + PUTTING TRANSACTION TOGETHER; OR 1?]]