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August 1997

An AnsiString class reference

by Kent Reisdorph

The AnsiString class (or String, for short) that comes with C++Builder is designed to work and play well with VCL. However, the documentation for the String class is somewhat lacking--OK, it's terrible. We'll do our best to remedy that situation in this article by describing the most commonly used String class operators, constructors, and functions. (We won't deal with wide-character support functions, however.)

Constructors

The String class includes constructors to let you create a String object from different data types. Table A shows the constructors and provides an example of each constructor's use.

Table A: String class constructors

Constructor	Description	Example
AnsiString();	Constructs an empty String object	String s;
AnsiString( const char* src);	Constructs a String object from a char* (a character array)	String ("This is a test"); char* buff = "Hello"; String s2(buff);
AnsiString( const AnsiString& src);	Constructs a String object from another String object	String s1 = "String One"; String s2(s1);
AnsiString( const char* src, unsigned char len);	Constructs a String object from a char* with the length specified in len	String s("", 255);
AnsiString(char src);	Constructs a String object from a char data type	char c = '\n'; String lf(c);
AnsiString(int src);	Constructs a String object from an int data type	int x = 200; String s(x);
AnsiString(double src);	Constructs a String object from a double data type	double d = 24.53; String s(d);

Operators

Table B shows the String operators and gives an example of each. These operators let you perform operations on strings using common-sense syntax rather than relying on cryptic function names.

Table B: String class operators

Operator	Description	Example
=	Assignment	s = "Test";
+	Concatentation	s = path + filename;
==	Equality	if (s == "Hello World")...
!=	Inequality	if (s != "Logon"). . .
<	Less than	if (s < "a")...
>	Greater than	if (s > "z")...
<=	Less than or =	if (s <= "1")...
>=	Greater than or =	if (s > = "10")...
[ ]	Index
Label1->Caption = s[10];

Primary functions

The String class's many functions let you manipulate strings just about any way you choose. We'll describe the functions you'll probably use most often with the String class.

AnsiCompare()

The AnsiCompare() function compares one string to another, using the following syntax:

int AnsiCompare(const AnsiString& rhs);

The return value will be -1 if the string is less than rhs, 1 if the string is greater than rhs, and 0 if the string's contents equal rhs. You don't use this function to test for equality, but rather to sort strings. For example,

String s1 = "Adam";

int result = s1.AnsiCompare("Bob");

In this case, result will be -1 because A is less than B. You can also use the < and > operators to sort strings.

AnsiCompareIC()

The AnsiCompareIC() function compares one string to another without regard to case sensitivity, using the following syntax:

int AnsiCompareIC(const AnsiString& rhs);

AnsiLastChar()

The AnsiLastChar() function uses the syntax

char* AnsiLastChar();

to return the last character in a string. For example, the code

String s = "This is a test";

Label1->Text = s.AnsiLastChar();

displays t in the Label component.

c_str()

The c_str() function returns a pointer to the character array used to hold the string's text. It uses this syntax:

char* __fastcall c_str();

You must use this function any time you need a char pointer to the string's text.

For example, the Windows API function DrawText() requires a pointer to a character buffer. In such a case, you'll need to use the c_str() function as follows:

DrawText(Canvas->Handle,

s.c_str(), s.Length(), &rect, DT_CALCRECT);

The c_str() function is also handy if you need to use a String object with the C-style string manipulation functions, such as strcpy().

Delete()

The Delete() function deletes count characters from the string beginning at index. The function's syntax is as follows:

void Delete(int index, int count);

In this example,

String s = "This is a test";

s.Delete(1, 5);

Label1->Caption = s;

the label will display is a test, since the code deletes the first five characters of the original string. Remember that the string indexing is 1-based, not 0-based.

Insert()

The Insert() function uses the syntax

void Insert(const AnsiString& str, int index);

to insert the string str starting at position index. For example, if you use the code

String s = "data.txt";

s.Insert("c:\\myprog\\", 1);

s will contain the text c:\myprog\data.txt after the call to Insert().

IsEmpty()

The IsEmpty() function has this syntax:

bool IsEmpty();

The function returns true if the string is empty and false if the string contains text.

IsPathDelimiter()

The IsPathDelimiter() function returns true if the character at the specified index is a backslash and false if it isn't. The function's syntax is as follows:

bool IsPathDelimiter(int index);

IsPathDelimiter() could be useful for traversing a string containing a path and filename.

LastDelimiter()

The LastDelimiter() function uses the following syntax:

int LastDelimiter(const AnsiString& delimiters);

You can use this function to find the last character specified in delimiters.

For instance, to extract just the path from a string containing a path and filename, you could use these lines:

String s = "c:\\myprog\\data.txt";

int pos = s.LastDelimiter("\\");

s.Delete(1, pos);

This code finds the last backslash in the string and then deletes everything from the beginning of the string to that position.

Length()

The Length() function returns the number of characters in the string. Its syntax is:

int Length();

The returned value will be the length of the text in the string, unless you've modified the length using the SetLength() function. The returned value doesn't include a terminating null character.

For example, you could use these lines:

String s = "Hello World";

int length = s.Length();

In this case, length will contain the value 11, since there are 11 actual characters in the text string.

LowerCase()

The LowerCase() function uses the syntax

AnsiString LowerCase();

This function converts the string to lowercase and returns the converted string. (However, it doesn't modify the text in the string object.) LowerCase() is useful for converting a string to lowercase (such as strings containing filenames) or for comparing two strings regardless of case.

For example, in the line

if (s1.LowerCase() == s2.LowerCase()) DoSomething();

the code doesn't modify the text in the strings--it simply compares the strings' lowercase representations for equality. If you actually want to convert a string to lowercase you'll need to use code like the following:

String s = "TEST";

s = s.LowerCase();

Pos()

The Pos() function uses the following syntax:

int Pos(const AnsiString& subStr);

It returns the position of the string passed in subStr. If the string can't be found, then Pos() returns 0. The AnsiPos() functions perform exactly the same way.

The following code finds the position of a substring within the target string:

String s = "This is a test";

int p = s.Pos("test");

Label1->Caption = "Pos: " + String(p);

This code will display the text Pos: 11 in the label component. Again, remember that the string index is 1-based, not 0-based.

SetLength()

You can use the SetLength() function to set the length of the buffer holding the string object's text. Its syntax is as follows:

void SetLength(int newLength);

Normally, the String class dynamically allocates space for the text in the string as needed, so there's rarely any reason to set the length yourself. For example:

String s; // length is 0

s = "test"; // length is 4

s.SetLength(50); // length is 50

s = "new string"; // length is 10

If you set the length to a value less than the current length of the text in the string, then the string will be truncated.

StringOfChar()

The StringOfChar() function has the following syntax:

AnsiString StringOfChar(char ch, int count);

This function creates a string filled with the character ch, with a length of count. For example, the following code fills a string with 20 spaces:

String s; s = s.StringOfChar(' ', 20); SubString()

The SubString() function uses this syntax:

AnsiString SubString(int index, int count);

It returns a substring of the string object starting at index and having a length of count. For example, if you execute the code

String s = "My name is BillyBob";

String sub = s.SubString(12, 8);

then the value of sub will be BillyBob.

ToDouble()

The ToDouble() function converts a string to a double and returns the result. The syntax is simply

double ToDouble();

If the string can't be converted to a double, then VCL throws an EConvertError exception. Here's an example:

String s = "123.456";

double d = s.ToDouble();

d *= .3;

In order for the string to be converted, it must contain a valid floating-point number and no alpha characters.

ToInt()

The ToInt() function converts a string to an integer value and returns the result. The syntax is as follows:

int ToInt();

For example,

String s = "123";

int i = s.ToInt();

If the string can't be converted, then VCL throws an EConvertError exception.

ToIntDef()

The ToIntDef() function converts a string to an integer value and returns the result. Its syntax is

int ToIntDef(int defaultValue);

If the string can't be converted, then the function returns the value supplied in defaultValue; VCL doesn't throw an exception.

Trim(), TrimLeft(), TrimRight()

The three Trim functions trim blank spaces from a string object and return the result, using the following syntaxes:

AnsiString Trim();

AnsiString TrimLeft();

AnsiString TrimRight();

The Trim() function removes both leading and trailing spaces, TrimLeft() removes leading spaces, and TrimRight() removes only trailing spaces. These functions don't modify the text in the string object.

In this example,

String editText = Edit1->Text;

editText = editText.Trim();

Properties such as Caption, Title, and Text are String properties. As a result, you can condense the example code to a single line:

String editText = Edit1->Text.Trim();

UpperCase()

The UpperCase() function converts a string to upper- case and returns the result. In the syntax

AnsiString UpperCase();

the string's text isn't modified as in the example

s = s.UpperCase();

Other functions

Now, let's take a look at some useful utility functions. You may use these functions from time to time in your work with the String class.

CurrToStr()

The CurrToStr() function converts a currency value to a string and returns the string. The function uses the syntax

AnsiString CurrToStr(Currency value);

which doesn't change the string object for which you call it, but rather formats and returns a string. For example, the lines

String s;

Currency c(19.95);

c *= 1.06; // add sales tax

Label1->Caption = s.CurrToStr(c);

won't modify the String object s.

CurrToStrF()

The CurrToStrF() function uses this syntax:

AnsiString CurrToStrF(Currency value, TStringFloatFormat format, int digits);

It converts a currency value to a string, applies formatting, and returns the string. The lines

String s;

Currency c(19.95);

c *= 1.06; // add sales tax

Label1->Caption = s.CurrToStrF(c, AnsiString::sffCurrency, 2);

display the text $21.15 in the label. The text is formatted for currency, including the dollar sign and two decimal places.

FloatToStrF()

The FloatToStrF() function formats and returns a floating point number, using this syntax:

AnsiString FloatToStrF(

long double value, TStringFloatFormat format, 

int precision, int digits);

The resulting string is based on the format, precision, and digits parameters. For example, the lines

String s;

float f = 2219.3446237795;

Label1->Caption = s.FloatToStrF(f, 

AnsiString::sffExponent, 8, 0);

format the given floating point value in scientific notation using eight-digit precision.

Format()

The Format() function builds a string using a format string and the supplied arguments. The syntax is as follows:

AnsiString Format(const AnsiString& format,const TVarRec *args, int size);

This function works in a way similar to the sprintf() and wsprintf() functions in C++. For example, the lines

String s = Format("%s%d, %d",

OPENARRAY(TVarRec, ("Values: ", 10, 20)));

Label1->Caption = s;

display the string Values: 10, 20 in the label. Notice that the OPENARRAY macro passes the values to the Format() function. This process is necessary because C++ doesn't have open arrays--however, AnsiString::Format() calls the VCL version of Format(), which takes an open array as a parameter.

The Format() function is one of the few cases in which Pascal and C++ just don't work well together. You can use one of two alternative methods for building the string from the previous example:

// example 1

char buff[20];

sprintf(buff, "Value: %d, %d", 10, 20);

String s = buff;



// example 2

String s = "Value: " + String(10) + ", " + String(20);

In my humble opinion, these methods are easier to use than the Format() function.

FmtLoadStr()

The FmtLoadStr() function is a combination of the Format() and LoadStr() functions. The syntax

AnsiString FmtLoadStr(int ident, const TVarRec *args, int size);

loads the string resource ident and formats it according to the value of the args parameter. See the descriptions of Format() and LoadStr() for more information.

IsDelimiter()

The IsDelimiter() function uses this syntax:

bool IsDelimiter(const AnsiString& delimiters, int index);

The function returns true if the character at index matches one of the characters in the string delimiters. Here's an example:

String s = "c:\\myprog\\data.txt";

if (s.IsDelimiter("\\", 3)) DoSomething();

The delimiters parameter can be a string of several delimiters you want to test against. For instance, if you wanted to check to see whether the character at position 10 was a space, a minus sign, a plus sign, a comma, or a dollar sign, you'd use this code:

String s = "This is a string";

bool test = s.IsDelimiter(" -+,$", 10);

LoadStr()

The LoadStr() function loads a string resource using the following syntax:

AnsiString LoadStr(int ident);

Of course, you must have a string table resource bound to your executable program, as does the following example:

String s;

s = s.LoadStr(100); //load string with ID of 100

Poor class design?

Note that the CurrToStr(), CurrToStrF(), FloatToStrF(), Format(), FormatFloat(), FrmtLoadString(), and LoadStr() functions really don't belong in the AnsiString class at all. They don't operate on the string object for which you call them, nor do they use the string object in any way. In addition, these functions are provided as standalone functions in the VCL Sysutils unit. It's always easier to use the standalone version of these functions rather than the AnsiString version, as shown in these two examples:

// method 1

String s;

s = s.LoadStr(ID_STRING1);



// method 2

String s = LoadStr(ID_STRING1);

I suspect that Borland put these functions into the AnsiString class at some early point in C++Builder's development, then forgot them later, when they were no longer necessary. Regardless, they're part of the AnsiString class and they're useful functions, so we've listed them here.

Kent Reisdorph is a editor of the C++Builder Developer's Journal as well as director of systems and services at TurboPower Software Company, and a member of TeamB, Borland's volunteer online support group. He's the author of Teach Yourself C++Builder in 21 Days and Teach Yourself C++Builder in 14 Days. You can contact Kent at editor@bridgespublishing.com.

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An optional entry point into a dynamic-link library (DLL). When the system starts or terminates a process or thread, it calls the entry-point function for each loaded DLL using the first thread of the process. The system also calls the entry-point function for a DLL when it is loaded or unloaded using the LoadLibrary and FreeLibrary functions.

Warning  There are serious limits on what you can do in a DLL entry point. To provide more complex initialization, create an initialization routine for the DLL. You can require applications to call the initialization routine before calling any other routines in the DLL. Alternatively, the initialization routine can create a file with an ACL that restricts access, and each routine in the DLL would call the initialization routine if the file does not exist.

BOOL WINAPI DllMain(









  HINSTANCE hinstDLL,









  DWORD fdwReason,









  LPVOID lpvReserved









);

Parameters

hinstDLL

[in] Handle to the DLL module. The value is the base address of the DLL. The HINSTANCE of a DLL is the same as the HMODULE of the DLL, so hinstDLL can be used in calls to functions that require a module handle.

fdwReason

[in] Indicates why the DLL entry-point function is being called. This parameter can be one of the following values.

Value	Meaning
DLL_PROCESS_ATTACH 1	The DLL is being loaded into the virtual address space of the current process as a result of the process starting up or as a result of a call to LoadLibrary. DLLs can use this opportunity to initialize any instance data or to use the TlsAlloc function to allocate a thread local storage (TLS) index.
DLL_THREAD_ATTACH 2	The current process is creating a new thread. When this occurs, the system calls the entry-point function of all DLLs currently attached to the process. The call is made in the context of the new thread. DLLs can use this opportunity to initialize a TLS slot for the thread. A thread calling the DLL entry-point function with DLL_PROCESS_ATTACH does not call the DLL entry-point function with DLL_THREAD_ATTACH. Note that a DLL's entry-point function is called with this value only by threads created after the DLL is loaded by the process. When a DLL is loaded using LoadLibrary, existing threads do not call the entry-point function of the newly loaded DLL.
DLL_THREAD_DETACH 3	A thread is exiting cleanly. If the DLL has stored a pointer to allocated memory in a TLS slot, it should use this opportunity to free the memory. The system calls the entry-point function of all currently loaded DLLs with this value. The call is made in the context of the exiting thread.
DLL_PROCESS_DETACH 0	The DLL is being unloaded from the virtual address space of the calling process as a result of unsuccessfully loading the DLL, termination of the process, or a call to FreeLibrary. The DLL can use this opportunity to call the TlsFree function to free any TLS indices allocated by using TlsAlloc and to free any thread local data. Note that the thread that receives the DLL_PROCESS_DETACH notification is not necessarily the same thread that received the DLL_PROCESS_ATTACH notification.

lpvReserved

[in] If fdwReason is DLL_PROCESS_ATTACH, lpvReserved is NULL for dynamic loads and non-NULL for static loads.

If fdwReason is DLL_PROCESS_DETACH, lpvReserved is NULL if FreeLibrary has been called or the DLL load failed and non-NULL if the process is terminating.

Return Value

When the system calls the DllMain function with the DLL_PROCESS_ATTACH value, the function returns TRUE if it succeeds or FALSE if initialization fails. If the return value is FALSE when DllMain is called because the process uses the LoadLibrary function, LoadLibrary returns NULL. (The system immediately calls your entry-point function with DLL_PROCESS_DETACH and unloads the DLL.) If the return value is FALSE when DllMain is called during process initialization, the process terminates with an error. To get extended error information, call GetLastError.

When the system calls the DllMain function with any value other than DLL_PROCESS_ATTACH, the return value is ignored.

Remarks

DllMain is a placeholder for the library-defined function name. You must specify the actual name you use when you build your DLL. For more information, see the documentation included with your development tools.

During initial process startup or after a call to LoadLibrary, the system scans the list of loaded DLLs for the process. For each DLL that has not already been called with the DLL_PROCESS_ATTACH value, the system calls the DLL's entry-point function. This call is made in the context of the thread that caused the process address space to change, such as the primary thread of the process or the thread that called LoadLibrary. Access to the entry point is serialized by the system on a process-wide basis. Threads in DllMain hold the loader lock so no additional DLLs can be dynamically loaded or initialized.

If the DLL's entry-point function returns FALSE following a DLL_PROCESS_ATTACH notification, it receives a DLL_PROCESS_DETACH notification and the DLL is unloaded immediately. However, if the DLL_PROCESS_ATTACH code throws an exception, the entry-point function will not receive the DLL_PROCESS_DETACH notification.

There are cases in which the entry-point function is called for a terminating thread even if the entry-point function was never called with DLL_THREAD_ATTACH for the thread:

• The thread was the initial thread in the process, so the system called the entry-point function with the DLL_PROCESS_ATTACH value.
• The thread was already running when a call to the LoadLibrary function was made, so the system never called the entry-point function for it.

When a DLL is unloaded from a process as a result of an unsuccessful load of the DLL, termination of the process, or a call to FreeLibrary, the system does not call the DLL's entry-point function with the DLL_THREAD_DETACH value for the individual threads of the process. The DLL is only sent a DLL_PROCESS_DETACH notification. DLLs can take this opportunity to clean up all resources for all threads known to the DLL.

If you terminate a process by calling TerminateProcess or TerminateJobObject, the DLLs of that process do not receive DLL_PROCESS_DETACH notifications. If you terminate a thread by calling TerminateThread, the DLLs of that thread do not receive DLL_THREAD_DETACH notifications.

The entry-point function should perform only simple initialization or termination tasks. It must not call the LoadLibrary or LoadLibraryEx function (or a function that calls these functions), because this may create dependency loops in the DLL load order. This can result in a DLL being used before the system has executed its initialization code. Similarly, the entry-point function must not call the FreeLibrary function (or a function that calls FreeLibrary) during process termination, because this can result in a DLL being used after the system has executed its termination code.

Because Kernel32.dll is guaranteed to be loaded in the process address space when the entry-point function is called, calling functions in Kernel32.dll does not result in the DLL being used before its initialization code has been executed. Therefore, the entry-point function can call functions in Kernel32.dll that do not load other DLLs. For example, DllMain can create synchronization objects such as critical sections and mutexes, and use TLS. Unfortunately, there is not a comprehensive list of safe functions in Kernel32.dll.

Windows 2000:  Do not create a named synchronization object in DllMain because the system will then load an additional DLL. This restriction does not apply to subsequent versions of Windows.

Calling functions that require DLLs other than Kernel32.dll may result in problems that are difficult to diagnose. For example, calling User, Shell, and COM functions can cause access violation errors, because some functions load other system components. Conversely, calling functions such as these during termination can cause access violation errors because the corresponding component may already have been unloaded or uninitialized.

Because DLL notifications are serialized, entry-point functions should not attempt to communicate with other threads or processes. Deadlocks may occur as a result.

For information on best practices when writing a DLL, see http://www.microsoft.com/whdc/driver/kernel/DLL_bestprac.mspx.

If your DLL is linked with the C run-time library (CRT), the entry point provided by the CRT calls the constructors and destructors for global and static C++ objects. Therefore, these restrictions for DllMain also apply to constructors and destructors and any code that is called from them.

Example Code

For an example, see Dynamic-Link Library Entry-Point Function.

Requirements

Client	Requires Windows Vista, Windows XP, Windows 2000 Professional, Windows NT Workstation, Windows Me, Windows 98, or Windows 95.
Server	Requires Windows Server "Longhorn", Windows Server 2003, Windows 2000 Server, or Windows NT Server.

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