constexpr string conversions

Signed-off-by: Rosen Penev <rosenp@gmail.com>

include/exiv2/basicio.hpp

@@ -690,12 +690,12 @@ namespace Exiv2 {
             @brief The extension of the temporary file which is created when getting input data
                     to read metadata. This file will be deleted in destructor.
         */
-        static const std::string TEMP_FILE_EXT;
+        static constexpr std::string_view TEMP_FILE_EXT = ".exiv2_temp";
         /*!
             @brief The extension of the generated file which is created when getting input data
                     to add or modify the metadata.
         */
-        static const std::string GEN_FILE_EXT;
+        static constexpr std::string_view GEN_FILE_EXT = ".exiv2";
 
         //! @name Creators
         //@{

src/basicio.cpp

@@ -53,7 +53,7 @@ namespace fs = std::filesystem;
 // class member definitions
 namespace {
     /// @brief replace each substring of the subject that matches the given search string with the given replacement.
-    void ReplaceStringInPlace(std::string& subject, const std::string& search, const std::string& replace)
+    void ReplaceStringInPlace(std::string& subject, std::string_view search, std::string_view replace)
     {
         auto pos = subject.find(search);
         while (pos != std::string::npos) {
@@ -946,9 +946,6 @@ namespace Exiv2 {
     }
 
 #else
-    const std::string XPathIo::TEMP_FILE_EXT = ".exiv2_temp";
-    const std::string XPathIo::GEN_FILE_EXT  = ".exiv2";
-
     XPathIo::XPathIo(const std::string& orgPath) : FileIo(XPathIo::writeDataToFile(orgPath)), isTemp_(true)
     {
         tempFilePath_ = path();

src/epsimage.cpp

@@ -33,7 +33,7 @@ namespace {
     using Exiv2::byte;
 
     // signature of DOS EPS
-    const std::string dosEpsSignature = "\xC5\xD0\xD3\xC6";
+    constexpr auto dosEpsSignature = std::string_view("\xC5\xD0\xD3\xC6");
 
     // first line of EPS
     constexpr auto epsFirstLine = std::array<std::string_view, 3>{
@@ -43,11 +43,12 @@ namespace {
     };
 
     // blank EPS file
-    const std::string epsBlank = "%!PS-Adobe-3.0 EPSF-3.0\n"
+    constexpr auto epsBlank = std::string_view(
-                                 "%%BoundingBox: 0 0 0 0\n";
+        "%!PS-Adobe-3.0 EPSF-3.0\n"
+        "%%BoundingBox: 0 0 0 0\n");
 
     // list of all valid XMP headers
-    const std::string xmpHeaders[] = {
+    constexpr std::string_view xmpHeaders[] = {
 
         // We do not enforce the trailing "?>" here, because the XMP specification
         // permits additional attributes after begin="..." and id="...".
@@ -67,11 +68,11 @@ namespace {
 
     // list of all valid XMP trailers
     struct XmpTrailer {
-        std::string trailer;
+        std::string_view trailer;
         bool readOnly;
     };
 
-    const XmpTrailer xmpTrailers[] = {
+    constexpr XmpTrailer xmpTrailers[] = {
 
         // We do not enforce the trailing "?>" here, because the XMP specification
         // permits additional attributes after end="...".
@@ -83,7 +84,7 @@ namespace {
     };
 
     // closing part of all valid XMP trailers
-    const std::string xmpTrailerEnd = "?>";
+    constexpr auto xmpTrailerEnd = std::string_view("?>");
 
     //! Write data into temp file, taking care of errors
     void writeTemp(BasicIo& tempIo, const byte* data, size_t size)
@@ -186,7 +187,7 @@ namespace {
                 for (size_t trailerPos = xmpPos + header.size(); trailerPos < size; trailerPos++) {
                     if (data[xmpPos] != '\x00' && data[xmpPos] != '<') continue;
                     for (auto&& xmpTrailer : xmpTrailers) {
-                        const std::string& trailer = xmpTrailer.trailer;
+                        auto trailer = xmpTrailer.trailer;
                         const bool readOnly = xmpTrailer.readOnly;
 
                         if (trailerPos + trailer.size() > size) continue;

src/pngimage.cpp

@@ -206,15 +206,14 @@ namespace Exiv2 {
         chType[4]=0;
 
         if ( option == kpsBasic || option == kpsXMP || option == kpsIccProfile || option == kpsRecursive ) {
-
+            constexpr auto xmpKey = "XML:com.adobe.xmp";
-            const std::string xmpKey  = "XML:com.adobe.xmp";
+            constexpr auto exifKey = "Raw profile type exif";
-            const std::string exifKey = "Raw profile type exif";
+            constexpr auto app1Key = "Raw profile type APP1";
-            const std::string app1Key = "Raw profile type APP1";
+            constexpr auto iptcKey = "Raw profile type iptc";
-            const std::string iptcKey = "Raw profile type iptc";
+            constexpr auto iccKey = "icc";
-            const std::string iccKey  = "icc";
+            constexpr auto softKey = "Software";
-            const std::string softKey = "Software";
+            constexpr auto commKey = "Comment";
-            const std::string commKey = "Comment";
+            constexpr auto descKey = "Description";
-            const std::string descKey = "Description";
 
             bool bPrint = option == kpsBasic || option == kpsRecursive ;
             if ( bPrint ) {

src/value.cpp

@@ -831,7 +831,7 @@ namespace Exiv2 {
         return value_.size();
     }
 
-    static const std::string x_default = "x-default";
+    static constexpr auto x_default = "x-default";
 
     std::ostream& LangAltValue::write(std::ostream& os) const
     {