Add an example on providing streams with CATCH_CONFIG_NOSTDOUT

Related to #1037
Closes #1290

examples/231-Cfg-OutputStreams.cpp

@@ -0,0 +1,49 @@
+// 231-Cfg-OutputStreams.cpp
+// Show how to replace the streams with a simple custom made streambuf.
+
+// Note that this reimplementation _does not_ follow `std::cerr`
+// semantic, because it buffers the output. For most uses however,
+// there is no important difference between having `std::cerr` buffered
+// or unbuffered.
+
+#define CATCH_CONFIG_NOSTDOUT
+#define CATCH_CONFIG_MAIN
+#include <catch2/catch.hpp>
+
+class out_buff : public std::stringbuf {
+    std::FILE* m_stream;
+public:
+    out_buff(std::FILE* stream) :m_stream(stream) {}
+    ~out_buff() { pubsync(); }
+    int sync() {
+        int ret = 0;
+        for (unsigned char c : str()) {
+            if (putc(c, m_stream) == EOF) {
+                ret = -1;
+                break;
+            }
+        }
+        // Reset the buffer to avoid printing it multiple times
+        str("");
+        return ret;
+    }
+};
+
+namespace Catch {
+    std::ostream& cout() {
+        static std::ostream ret(new out_buff(stdout));
+        return ret;
+    }
+    std::ostream& clog() {
+        static std::ostream ret(new out_buff(stderr));
+        return ret;
+    }
+    std::ostream& cerr() {
+        return clog();
+    }
+}
+
+
+TEST_CASE("This binary uses putc to write out output", "[compilation-only]") {
+    SUCCEED("Nothing to test.");
+}

examples/CMakeLists.txt

@@ -17,6 +17,7 @@ set( HEADER_DIR   ${CATCH_DIR}/single_include )
 
 set( SOURCES_SINGLE_FILE
     010-TestCase.cpp
+    231-Cfg-OutputStreams.cpp
 )
 
 # multiple-file modules: