const string& 和const string之间有不同吗?
//---------------------------------------------------------------------------
#include <vcl.h>
#pragma hdrstop
#include "Unit1.h"
#include <string>
#include <ctype>
using std::string;
//---------------------------------------------------------------------------
#pragma package(smart_init)
#pragma resource "*.dfm"
TForm1 *Form1;
string UC(const string& s)
{
s.append("在过程中添加数据");
string r(s);
for (std::size_t i=0;i!=s.size() ;++i) {
r[i]=tolower(s[i]);
}
return r;
}
string NoUC(const string s)
{
s.append("在过程中添加数据");
string r(s);
for (std::size_t i=0;i!=s.size() ;++i) {
r[i]=tolower(s[i]);
}
return r;
}
//---------------------------------------------------------------------------
__fastcall TForm1::TForm1(TComponent* Owner)
: TForm(Owner)
{
}
//---------------------------------------------------------------------------
void __fastcall TForm1::btn1Click(TObject *Sender)
{
string s, ss="aaa ";
s = UC(ss);
Application->MessageBox(s.c_str(), "s", MB_OK);
Application->MessageBox(ss.c_str(), "ss", MB_OK);
}
//---------------------------------------------------------------------------
void __fastcall TForm1::btn2Click(TObject *Sender)
{
string s, ss="aaa ";
s = NoUC(ss);
Application->MessageBox(s.c_str(), "s", MB_OK);
Application->MessageBox(ss.c_str(), "ss", MB_OK);
}
//---------------------------------------------------------------------------
为什么结果不一样,很多书上都要求加&,说不会改变内里值,但是这里是为什么...