diff --git a/camera/provider/2.4/default/ExternalCameraProviderImpl_2_4.cpp b/camera/provider/2.4/default/ExternalCameraProviderImpl_2_4.cpp
index 4fc7437..04db7f3 100644
--- a/camera/provider/2.4/default/ExternalCameraProviderImpl_2_4.cpp
+++ b/camera/provider/2.4/default/ExternalCameraProviderImpl_2_4.cpp
@@ -18,15 +18,16 @@
 //#define LOG_NDEBUG 0
 #include <log/log.h>
 
-#include <regex>
-#include <sys/inotify.h>
+#include <cutils/properties.h>
 #include <errno.h>
 #include <linux/videodev2.h>
-#include <cutils/properties.h>
-#include "ExternalCameraProviderImpl_2_4.h"
+#include <sys/inotify.h>
+#include <regex>
+#include <string>
 #include "ExternalCameraDevice_3_4.h"
 #include "ExternalCameraDevice_3_5.h"
 #include "ExternalCameraDevice_3_6.h"
+#include "ExternalCameraProviderImpl_2_4.h"
 
 namespace android {
 namespace hardware {
@@ -41,10 +42,10 @@
 // "device@<version>/external/<id>"
 const std::regex kDeviceNameRE("device@([0-9]+\\.[0-9]+)/external/(.+)");
 const int kMaxDevicePathLen = 256;
-const char* kDevicePath = "/dev/";
-constexpr char kPrefix[] = "video";
-constexpr int kPrefixLen = sizeof(kPrefix) - 1;
-constexpr int kDevicePrefixLen = sizeof(kDevicePath) + kPrefixLen + 1;
+constexpr const char* kDevicePath = "/dev/";
+constexpr const char* kPrefix = "video";
+constexpr int kPrefixLen = std::char_traits<char>::length(kPrefix);
+constexpr int kDevicePrefixLen = std::char_traits<char>::length(kDevicePath) + kPrefixLen;
 
 bool matchDeviceName(int cameraIdOffset,
                      const hidl_string& deviceName, std::string* deviceVersion,
diff --git a/camera/provider/2.7/default/ExternalCameraProviderImpl_2_7.cpp b/camera/provider/2.7/default/ExternalCameraProviderImpl_2_7.cpp
index b63e3bb..62ce074 100644
--- a/camera/provider/2.7/default/ExternalCameraProviderImpl_2_7.cpp
+++ b/camera/provider/2.7/default/ExternalCameraProviderImpl_2_7.cpp
@@ -23,6 +23,7 @@
 #include <linux/videodev2.h>
 #include <sys/inotify.h>
 #include <regex>
+#include <string>
 #include "ExternalCameraDevice_3_4.h"
 #include "ExternalCameraDevice_3_5.h"
 #include "ExternalCameraDevice_3_6.h"
@@ -39,10 +40,10 @@
 // "device@<version>/external/<id>"
 const std::regex kDeviceNameRE("device@([0-9]+\\.[0-9]+)/external/(.+)");
 const int kMaxDevicePathLen = 256;
-const char* kDevicePath = "/dev/";
-constexpr char kPrefix[] = "video";
-constexpr int kPrefixLen = sizeof(kPrefix) - 1;
-constexpr int kDevicePrefixLen = sizeof(kDevicePath) + kPrefixLen + 1;
+constexpr const char* kDevicePath = "/dev/";
+constexpr const char* kPrefix = "video";
+constexpr int kPrefixLen = std::char_traits<char>::length(kPrefix);
+constexpr int kDevicePrefixLen = std::char_traits<char>::length(kDevicePath) + kPrefixLen;
 
 bool matchDeviceName(int cameraIdOffset, const hidl_string& deviceName, std::string* deviceVersion,
                      std::string* cameraDevicePath) {