replace [0] with front() where applicable

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

src/basicio.cpp

@@ -1467,7 +1467,7 @@ void HttpIo::HttpImpl::writeRemote(const byte* data, size_t size, size_t from, s
 
   // standardize the path without "/" at the beginning.
   std::size_t protocolIndex = scriptPath.find("://");
-  if (protocolIndex == std::string::npos && scriptPath[0] != '/') {
+  if (protocolIndex == std::string::npos && scriptPath.front() != '/') {
     scriptPath = "/" + scriptPath;
   }
 
@@ -1657,7 +1657,7 @@ void CurlIo::CurlImpl::writeRemote(const byte* data, size_t size, size_t from, s
   // add the protocol and host to the path
   std::size_t protocolIndex = scriptPath.find("://");
   if (protocolIndex == std::string::npos) {
-    if (scriptPath[0] != '/')
+    if (scriptPath.front() != '/')
       scriptPath = "/" + scriptPath;
     scriptPath = hostInfo.Protocol + "://" + hostInfo.Host + scriptPath;
   }

src/epsimage.cpp

@@ -475,7 +475,7 @@ void readWriteEpsMetadata(BasicIo& io, std::string& xmpPacket, NativePreviewList
 #endif
     // implicit comments
     if (line == "%%EOF" || line == "%begin_xml_code" ||
-        !(line.size() >= 2 && line[0] == '%' && '\x21' <= line[1] && line[1] <= '\x7e')) {
+        !(line.size() >= 2 && line.front() == '%' && '\x21' <= line[1] && line[1] <= '\x7e')) {
       if (posEndComments == posEndEps) {
         posEndComments = startPos;
 #ifdef DEBUG
@@ -492,20 +492,21 @@ void readWriteEpsMetadata(BasicIo& io, std::string& xmpPacket, NativePreviewList
 #endif
     }
     if (posBeginPageSetup == posEndEps &&
-        (implicitPage || (posPage != posEndEps && !inRemovableEmbedding && !line.empty() && line[0] != '%'))) {
+        (implicitPage || (posPage != posEndEps && !inRemovableEmbedding && !line.empty() && line.front() != '%'))) {
       posBeginPageSetup = startPos;
       implicitPageSetup = true;
 #ifdef DEBUG
       EXV_DEBUG << "readWriteEpsMetadata: Found implicit BeginPageSetup at position: " << startPos << "\n";
 #endif
     }
-    if (posEndPageSetup == posEndEps && implicitPageSetup && !inRemovableEmbedding && !line.empty() && line[0] != '%') {
+    if (posEndPageSetup == posEndEps && implicitPageSetup && !inRemovableEmbedding && !line.empty() &&
+        line.front() != '%') {
       posEndPageSetup = startPos;
 #ifdef DEBUG
       EXV_DEBUG << "readWriteEpsMetadata: Found implicit EndPageSetup at position: " << startPos << "\n";
 #endif
     }
-    if (!line.empty() && line[0] != '%')
+    if (!line.empty() && line.front() != '%')
       continue;  // performance optimization
     if (line == "%%EOF" || line == "%%Trailer" || line == "%%PageTrailer") {
       if (posBeginPageSetup == posEndEps) {

src/makernote_int.cpp

@@ -120,7 +120,7 @@ const TiffMnRegistry TiffMnCreator::registry_[] = {
 
 bool TiffMnRegistry::operator==(const std::string& key) const {
   std::string make(make_);
-  if (!key.empty() && key[0] == '-')
+  if (!key.empty() && key.front() == '-')
     return false;
   return make == key.substr(0, make.length());
 }

src/tags_int.cpp

@@ -31,8 +31,8 @@ std::ostream& printVersion(std::ostream& os, const std::string& str) {
   if (str.size() != 4) {
     return os << "(" << str << ")";
   }
-  if (str[0] != '0')
-    os << str[0];
+  if (str.front() != '0')
+    os << str.front();
   return os << str[1] << "." << str[2] << str[3];
 }
 }  // namespace

src/value.cpp

@@ -323,7 +323,7 @@ int CommentValue::read(const std::string& comment) {
     const std::string::size_type pos = comment.find_first_of(' ');
     std::string name = comment.substr(8, pos - 8);
     // Strip quotes (so you can also specify the charset without quotes)
-    if (!name.empty() && name[0] == '"')
+    if (!name.empty() && name.front() == '"')
       name = name.substr(1);
     if (!name.empty() && name[name.length() - 1] == '"')
       name = name.substr(0, name.length() - 1);
@@ -499,7 +499,7 @@ int XmpTextValue::read(const std::string& buf) {
     std::string::size_type pos = buf.find_first_of(' ');
     type = buf.substr(5, pos - 5);
     // Strip quotes (so you can also specify the type without quotes)
-    if (!type.empty() && type[0] == '"')
+    if (!type.empty() && type.front() == '"')
       type = type.substr(1);
     if (!type.empty() && type[type.length() - 1] == '"')
       type = type.substr(0, type.length() - 1);
@@ -662,7 +662,7 @@ int LangAltValue::read(const std::string& buf) {
     if (lang.empty())
       throw Error(ErrorCode::kerInvalidLangAltValue, buf);
     // Strip quotes (so you can also specify the language without quotes)
-    if (lang[0] == '"') {
+    if (lang.front() == '"') {
       lang = lang.substr(1);
 
       if (lang.empty() || lang.find('"') != lang.length() - 1)