動作環境

C++ Builder XE4

関連 http://qiita.com/7of9/items/4caba5c87522aa410447
関連 http://qiita.com/7of9/items/490f6b00b197f4e7df6e

TLabelを用意した時、そこにどの長さまでString文字列を代入できるか確認したくなった。

以下のgetMaximumStringLength()を実装した。

Unit1.cpp

//---------------------------------------------------------------------------

# include <vcl.h>
# pragma hdrstop

# include "Unit1.h"
//---------------------------------------------------------------------------
# pragma package(smart_init)
# pragma resource "*.dfm"
TForm1 *Form1;
//---------------------------------------------------------------------------
__fastcall TForm1::TForm1(TComponent* Owner)
	: TForm(Owner)
{
}
//---------------------------------------------------------------------------
void __fastcall TForm1::Button1Click(TObject *Sender)
{
//	String kDummyString = L"START_jfkldsajkfjdklsajfkldjsklfjaksdljfkldsjalkjfsdk_END";

//	Label1->Caption = kDummyString;

	int mxlen = getMaximumStringLength(Label1);
	String msg = L"Maxsize:" + IntToStr(mxlen);
	OutputDebugString(msg.c_str());

//	fitWithDesignedWidth(Label1);


	int nop=1;
}
//---------------------------------------------------------------------------

void __fastcall TForm1::fitWithDesignedWidth(TLabel *lblPtr)
{
	int fntsiz[] = { 16, 14, 12, 10, 8 }; // 大きいサイズから
	int size = sizeof(fntsiz) / sizeof(fntsiz[0]);

	bool widthIsOk;

	for(int idx=0; idx<size; idx++) {
		lblPtr->Font->Size = fntsiz[idx];
		widthIsOk = checkWidthIsLargeEnough(lblPtr);
		if (widthIsOk) {
			break;
		}
	}
}

int __fastcall TForm1::getMaximumStringLength(TLabel *lblPtr)
{
	static const int kMaxLoop = 8;
	static const int kIncrease = 5;

	bool widthIsOk;
	int maxLen = 10;

	lblPtr->Caption = L"1234567890";

	int loop = 0;
	while(loop < kMaxLoop) {
		lblPtr->Caption = lblPtr->Caption + L"SAAAE"; // [kIncrease]に合わせて文字を用意
		widthIsOk = checkWidthIsLargeEnough(lblPtr);
		if (widthIsOk == false) {
			lblPtr->Caption = lblPtr->Caption.SubString(0, lblPtr->Caption.Length() - kIncrease);
			break;
		}
		maxLen += kIncrease;
		loop++;
	}

	return maxLen;
}

bool __fastcall TForm1::checkWidthIsLargeEnough(TLabel *lblPtr)
{
	int orgWdt = lblPtr->Width;

	// to check
	lblPtr->AutoSize = true;
	int aftWdt = Label1->Width;

	// recover
	lblPtr->AutoSize = false;
	lblPtr->Width = orgWdt;

	return (aftWdt < orgWdt);
}

結果

デバッグ出力: Maxsize:30 プロセス Project1.exe (752)