Add client example

example/client.cpp

@@ -0,0 +1,113 @@
+/**
+ * Copyright - See the COPYRIGHT that is included with this distribution.
+ * pvxs is distributed subject to a Software License Agreement found
+ * in file LICENSE that is included with this distribution.
+ */
+/** Meant to be run against the mailbox example.
+ *  eg. in one terminal run:
+ *
+ *   ./mailbox some:pv:name
+ *
+ * And in another terminal run:
+ *
+ *   ./client some:pv:name
+ */
+
+#include <iostream>
+
+#include <pvxs/client.h>
+#include <pvxs/log.h>
+
+using namespace pvxs;
+
+int main(int argc, char* argv[])
+{
+    if(argc<2) {
+        std::cerr<<"Usage: "<<argv[0]<<" <pvname>\n";
+        return 1;
+    }
+
+    // Read $PVXS_LOG from process environment and update
+    // logging configuration.  eg.
+    //    export PVXS_LOG=*=DEBUG
+    // makes a lot of noise.
+    logger_config_env();
+
+    // Create a client context
+    client::Context ctxt(client::Config::from_env()
+                         .build());
+
+    // Fetch current value
+    int32_t current;
+    {
+        std::cout<<"Getting current value of '"<<argv[1]<<"'"<<std::endl;
+        // Build and start network operation
+        auto op = ctxt.get(argv[1])
+                .exec();
+
+        // wait for it to complete, for up to 5 seconds.
+        Value result = op->wait(5.0);
+
+        std::cout<<"Result is:\n"<<result<<std::endl;
+
+        if(auto value = result["value"]) {
+            // there is a .value field
+            // as may still throw pvxs::NoConvert if its value can't
+            // be converted to int32_t
+            current = value.as<int32_t>();
+        } else {
+            // an example.  won't happen with mailbox server
+            std::cerr<<"Server type doesn't have .value field!\n";
+            return 1;
+        }
+    }
+
+    {
+        // attempt to change.
+        // uses simple builder form to assign .value
+
+        ctxt.put(argv[1])
+                .fetchPresent(false) // not needed
+                .set("value", current+1)
+                .exec()
+                ->wait(5.0);
+
+        std::cout<<"First increment successful"<<std::endl;
+    }
+
+    {
+        // change again.
+        // use build() callback
+
+        auto op = ctxt.put(argv[1])
+                // provide present value to build() callback.
+                .fetchPresent(true)
+                .build([](Value&& current) -> Value {
+                    // allocate an empty container
+                    auto toput(current.cloneEmpty());
+
+                    // fill in .value.
+                    // Assignment implicitly marks .value as changed
+                    toput["value"] = current["value"].as<int32_t>() + 1;
+
+                    // return the container to be sent
+                    return toput;
+                })
+                .exec();
+
+        op->wait(5.0);
+
+        std::cout<<"Second increment successful"<<std::endl;
+    }
+
+    // fetch final value
+    {
+        std::cout<<"Getting current value of '"<<argv[1]<<"'"<<std::endl;
+        // Build and start network operation
+        auto result = ctxt.get(argv[1])
+                .exec()
+                ->wait(5.0);
+
+        std::cout<<"Result is:\n"<<result<<std::endl;
+    }
+}