小优化：减少内存分配次数

work20220407/string/String.cpp

@@ -25,7 +25,7 @@ String::String() : String(128) {}
 String::String(const char *source) : String(source, (int) strlen(source)) {}
 
 /**
- * 从源中复制字符串来构建新的对象，并定义初始长度，小于源字符串则会被截取
+ * 从源中复制字符串来构建新的对象，并定义字符串实际长度，小于源字符串则会被截取
  */
 String::String(const char *source, int length) : String(length + 1) {
     strncpy(data, source, length);
@@ -152,8 +152,6 @@ void String::addString(const char *source, int sourceLength) {
         this->data = new char[allocSize]();
 
         length = sourceLength;
-    } else {
-        length = (int) strlen(data);
     }
 
     // 如果拼接后字符长度超过已分配的内存大小，则重新分配data内存大小
@@ -162,17 +160,17 @@ void String::addString(const char *source, int sourceLength) {
         char *old = new char[length + 1]();
         strcpy(old, data);
 
-
         // 重新分配内存，防止拼接后溢出
+        // 分配两倍内存空间来减少重新分配次数
         delete[] data;
-        allocSize = length + sourceLength + 1;
+        allocSize = (length + sourceLength)*2 + 1;
         this->data = new char[allocSize]();
 
         strcpy(data, old);
     }
 
     strcat(data, source);
-    length = allocSize - 1;
+    length += sourceLength;
 }
 
 /**
@@ -217,14 +215,16 @@ char &String::operator[](int i) {
 String String::operator+(const char *source) {
     int sourceLength = (int) strlen(source);
 
-    String target(this->data, this->length + sourceLength + 1);
+    String target = String((this->length + sourceLength)*2 + 1);
+    target = this->data;
     target += source;
 
     return target;
 }
 
 String String::operator+(const String &source) {
-    String target(this->data, this->length + source.length);
+    String target = String((this->length + source.length)*2 + 1);
+    target = this->data;
     target += source;
 
     return target;