Use the character based overload for std::string::find.

std::string::find has a character based overload as can be seen here
(4th oveload): http://www.cplusplus.com/reference/string/string/find/

Use that instead of constantly allocating temporary strings.

src/bitcoin-tx.cpp

@@ -305,8 +305,8 @@ static void MutateTxAddOutPubKey(CMutableTransaction& tx, const std::string& str
     bool bScriptHash = false;
     if (vStrInputParts.size() == 3) {
         std::string flags = vStrInputParts[2];
-        bSegWit = (flags.find("W") != std::string::npos);
-        bScriptHash = (flags.find("S") != std::string::npos);
+        bSegWit = (flags.find('W') != std::string::npos);
+        bScriptHash = (flags.find('S') != std::string::npos);
     }
 
     if (bSegWit) {
@@ -367,8 +367,8 @@ static void MutateTxAddOutMultiSig(CMutableTransaction& tx, const std::string& s
     bool bScriptHash = false;
     if (vStrInputParts.size() == numkeys + 4) {
         std::string flags = vStrInputParts.back();
-        bSegWit = (flags.find("W") != std::string::npos);
-        bScriptHash = (flags.find("S") != std::string::npos);
+        bSegWit = (flags.find('W') != std::string::npos);
+        bScriptHash = (flags.find('S') != std::string::npos);
     }
     else if (vStrInputParts.size() > numkeys + 4) {
         // Validate that there were no more parameters passed
@@ -447,8 +447,8 @@ static void MutateTxAddOutScript(CMutableTransaction& tx, const std::string& str
     bool bScriptHash = false;
     if (vStrInputParts.size() == 3) {
         std::string flags = vStrInputParts.back();
-        bSegWit = (flags.find("W") != std::string::npos);
-        bScriptHash = (flags.find("S") != std::string::npos);
+        bSegWit = (flags.find('W') != std::string::npos);
+        bScriptHash = (flags.find('S') != std::string::npos);
     }
 
     if (scriptPubKey.size() > MAX_SCRIPT_SIZE) {

src/httprpc.cpp

@@ -85,11 +85,11 @@ static void JSONErrorReply(HTTPRequest* req, const UniValue& objError, const Uni
 //entries from config file.
 static bool multiUserAuthorized(std::string strUserPass)
 {    
-    if (strUserPass.find(":") == std::string::npos) {
+    if (strUserPass.find(':') == std::string::npos) {
         return false;
     }
-    std::string strUser = strUserPass.substr(0, strUserPass.find(":"));
-    std::string strPass = strUserPass.substr(strUserPass.find(":") + 1);
+    std::string strUser = strUserPass.substr(0, strUserPass.find(':'));
+    std::string strPass = strUserPass.substr(strUserPass.find(':') + 1);
 
     for (const std::string& strRPCAuth : gArgs.GetArgs("-rpcauth")) {
         //Search for multi-user login/pass "rpcauth" from config
@@ -132,8 +132,8 @@ static bool RPCAuthorized(const std::string& strAuth, std::string& strAuthUserna
     boost::trim(strUserPass64);
     std::string strUserPass = DecodeBase64(strUserPass64);
 
-    if (strUserPass.find(":") != std::string::npos)
-        strAuthUsernameOut = strUserPass.substr(0, strUserPass.find(":"));
+    if (strUserPass.find(':') != std::string::npos)
+        strAuthUsernameOut = strUserPass.substr(0, strUserPass.find(':'));
 
     //Check if authorized under single-user field
     if (TimingResistantEqual(strUserPass, strRPCUserColonPass)) {

src/rest.cpp

@@ -423,8 +423,8 @@ static bool rest_getutxos(HTTPRequest* req, const std::string& strURIPart)
         {
             uint256 txid;
             int32_t nOutput;
-            std::string strTxid = uriParts[i].substr(0, uriParts[i].find("-"));
-            std::string strOutput = uriParts[i].substr(uriParts[i].find("-")+1);
+            std::string strTxid = uriParts[i].substr(0, uriParts[i].find('-'));
+            std::string strOutput = uriParts[i].substr(uriParts[i].find('-')+1);
 
             if (!ParseInt32(strOutput, &nOutput) || !IsHex(strTxid))
                 return RESTERR(req, HTTP_BAD_REQUEST, "Parse error");

src/rpc/client.cpp

@@ -213,7 +213,7 @@ UniValue RPCConvertNamedValues(const std::string &strMethod, const std::vector<s
     UniValue params(UniValue::VOBJ);
 
     for (const std::string &s: strParams) {
-        size_t pos = s.find("=");
+        size_t pos = s.find('=');
         if (pos == std::string::npos) {
             throw(std::runtime_error("No '=' in named argument '"+s+"', this needs to be present for every argument (even if it is empty)"));
         }

src/rpc/net.cpp

@@ -516,7 +516,7 @@ UniValue setban(const JSONRPCRequest& request)
     CNetAddr netAddr;
     bool isSubnet = false;
 
-    if (request.params[0].get_str().find("/") != std::string::npos)
+    if (request.params[0].get_str().find('/') != std::string::npos)
         isSubnet = true;
 
     if (!isSubnet) {