Adding support for reading Environmental variable for samples (#186)

* check if env var set and choose device

* clean up for env var

* app modification

* move getEnvVar function to header

* fork example

* spacing adjust

* review comments

* use hipGetErrorName to throw errors

[ROCm/rocdecode commit: 8ec38d2d24]

projects/rocdecode/utils/rocvideodecode/roc_video_dec.cpp

@@ -1078,3 +1078,15 @@ bool RocVideoDecoder::InitHIP(int device_id) {
     HIP_API_CALL(hipStreamCreate(&hip_stream_));
     return true;
 }
+
+int GetEnvVar(const char *name, int &dev_count) {
+    char *v = std::getenv(name);
+    if (v) {
+        char* p_tkn = std::strtok(v, ",");
+        while (p_tkn != nullptr) {
+            dev_count++;
+            p_tkn = strtok(nullptr, ",");
+        }
+    }
+    return dev_count;
+}

projects/rocdecode/utils/rocvideodecode/roc_video_dec.h

@@ -33,6 +33,7 @@ THE SOFTWARE.
 #include <queue>
 #include <stdexcept>
 #include <exception>
+#include <cstring>
 #include <hip/hip_runtime.h>
 extern "C" {
 #include "libavutil/md5.h"
@@ -149,6 +150,8 @@ typedef struct ReconfigParams_t {
     uint32_t reconfig_flush_mode;
 } ReconfigParams;
 
+int GetEnvVar(const char *name, int &dev_count);
+
 class RocVideoDecoder {
     public:
       /**