fix: string bugs

src/lib/stl/string.cpp

@@ -28,10 +28,10 @@ String::String(int length):_capacity(length+1),_length(length){
 }
 
 String::String(const String& b){
-    _capacity=b._length;
+    _capacity=b._length+1;
     _length=b._length;
-    data=new char[_length];
-    memcpy(data,b.data,_length);
+    data=new char[_capacity];
+    memcpy(data,b.data,_capacity);
 }
 
 char* String::c_str()const{
@@ -39,11 +39,11 @@ char* String::c_str()const{
 }
 
 int String::length()const{
-    return _length-1;
+    return _length;
 }
 
 int String::size()const{
-    return _length-1;
+    return _length;
 }
 
 String String::operator+(const String& b)const{

src/lib/stl/string.h

@@ -6,8 +6,8 @@
 class String{
 public:
     const static int __INIT_CAPACITY=10;
-    int _capacity;
-    int _length;
+    int _capacity; // current vector capacity
+    int _length; // length without '0' in the end
     char* data;
 
     String(const char* str);