Removed unnecessary copying

Author: ankane

include/pgvector/pqxx.hpp

@@ -120,27 +120,32 @@ template <> struct string_traits<pgvector::SparseVector> {
         std::vector<int> indices;
         std::vector<float> values;
 
-        if (n > 1) {
-            std::istringstream ss(std::string(text.substr(1, n - 1)));
-            while (ss.good()) {
-                std::string substr;
-                std::getline(ss, substr, ',');
-
-                size_t ne = substr.find(":");
-                if (ne == std::string::npos) {
-                    throw conversion_error("Malformed sparsevec literal");
-                }
+        auto cb = [&](std::string_view substr) {
+            size_t ne = substr.find(":");
+            if (ne == std::string::npos) {
+                throw conversion_error("Malformed sparsevec literal");
+            }
 
-                int index = string_traits<int>::from_string(substr.substr(0, ne), c);
-                float value = string_traits<float>::from_string(substr.substr(ne + 1), c);
+            int index = string_traits<int>::from_string(substr.substr(0, ne), c);
+            float value = string_traits<float>::from_string(substr.substr(ne + 1), c);
 
-                if (index < 1) {
-                    throw conversion_error("Index out of bounds");
-                }
+            if (index < 1) {
+                throw conversion_error("Index out of bounds");
+            }
+
+            indices.push_back(index - 1);
+            values.push_back(value);
+        };
 
-                indices.push_back(index - 1);
-                values.push_back(value);
+        if (n > 1) {
+            size_t start = 1;
+            for (size_t i = start; i < n - 1; i++) {
+                if (text[i] == ',') {
+                    cb(text.substr(start, i - start));
+                    start = i + 1;
+                }
             }
+            cb(text.substr(start, n - start));
         }
 
         return pgvector::SparseVector(dimensions, indices, values);