strstr -> strchr

https://www.viva64.com/en/w/V817/print/

src/lib_json/json_writer.cpp

@@ -153,7 +153,7 @@ JSONCPP_STRING valueToString(double value, bool useSpecialFloats, unsigned int p
     fixNumericLocale(buffer, buffer + len);
 
     // try to ensure we preserve the fact that this was given to us as a double on input
-    if (!strstr(buffer, ".") && !strstr(buffer, "e")) {
+    if (!strchr(buffer, '.') && !strchr(buffer, 'e')) {
       strcat(buffer, ".0");
     }