Convert: char *, char [], cstring, the relationship between strings and some common functions

Original article address:Convert: char *,
Char [] , Cstring, String Conversion Author:Gisldq

(1) Overview

String and cstring are both string template classes. string is a string class defined by the standard template class (STL) and has been incorporated into the C ++ standard;

Cstring (typedef cstringt> cstring) is the most common string class in Visual C ++. It inherits from the csimplestringt class and is mainly used in MFC and ATL programming, the main data types include char (used in ANSI), wchar_t (UNICODE), and tchar (both ANSI and Unicode );

Char * is the most commonly used string pointer in C programming. It generally ends;

(2) Construction

String is convenient and can be constructed from almost all strings, including cstring and char *;

Followed by cstring, which can be constructed from some basic string variables, including char;

Char * has no constructor and can only be assigned a value;

Example:

Char * psz = "joise ";

Cstring CSTR (psz );

String STR (CSTR );

(3) Operator Overloading

A) operator =

String is the most convenient, and almost all strings can be assigned directly, including cstring and char *;

Followed by cstring. You can directly assign values using some basic strings, including char;

Char * can only be assigned values by pointers, which is extremely dangerous. We recommend that you use strcpy or memcpy. In addition, if the initial value is not assigned to char *, we recommend that you set it to null first, to avoid wild pointers and drive you crazy;

Example:

Char * psz = NULL;

Psz = new char [10]; // Of course, the above is directly written as char * psz = new char [10 ];

Memset (psz, 0, 10 );

Strcpy (psz, "joise ");

Cstring CSTR;

CSTR = psz;

String STR;

STR = psz;

STR = CSTR;

Delete [] psz;

B) operator +

String is similar to cstring. It can be added directly to char *, but the + operator cannot be used with each other. That is, string STR = STR + CSTR is invalid and must be converted to char *;

Char * has no + operation. Only two pointers can be connected using strcat;

Example:

Char * psz = "joise ";

Cstring CSTR = psz;

CSTR = CSTR + psz;

String STR = psz;

STR = STR + psz;

Strcat (psz, psz );

Strcat (psz, CSTR); // valid

Strcat (psz, STR); // invalid. Therefore, cstring can be automatically converted to const char *, but string cannot.

C) operator ++ =

String is the most powerful and can be used with almost all string variables + =, including cstring and char *;

Followed by cstring, which can be + = with some basic string variables, including char;

Char * has no + = Operator and can only use strcat to connect two pointers;

D) operator []

The cstring is the best. When a cross-border request is made, an asserted exception is thrown;

The results of the out-of-bounds string and char * subscripts are undefined;

Example:

Char * psz = "joise ";

Cstring CSTR = psz;

Cout <CSTR [8];

String STR = psz;

Cout <STR [8];

Cout <psz [8];

E) operator =, Operator! =, Operator>, operator <, operator> =, perator <=

Cstring and string cannot be compared, but both can be compared with char * and compared with the value rather than the address;

Cout <(psz = CSTR );

Cout <(psz = Str );

Cout <(STR = psz );

Cout <(CSTR = psz); // The code above returns 1

(4) common algorithms

A) Search

Function	Char *	String	Cstring
Search for a specified value	Strchr Strstr Strrstr Strspns	Find	Find
The first matched Value		Fild_first_of	Findoneof
Start searching later			Reservefind
Matching Method		Find_if

Note: In find_if, values in the range are substituted into the matching function one by one until true is returned.

B) Comparison

Function	Char *	String	Cstring
Search for a specified value (case sensitive)	Strcmp Strncmp Strcoll _ Strncoll	Operator < Operator> Operator <= Operator> = Operator = Operator! =	Collate Compare
Search for the specified value (Case Insensitive)	_ Stricmp _ Strnicmp _ Stricoll _ Strnicoll		Collatenocase Comparenocas

Note: If the return value is <0, the previous value is smaller than the subsequent value, and vice versa.

C) replace

Function	Char *	String	Cstring
Search for a specified value	_ Strset _ Strnset	Replace Replace_copy Replace_copy_if Replace_if	Replace

D) insert

Function	Char *	String	Cstring
Search for a specified value		Insert	Insert

E) add

Function	Char *	String	Cstring
Dynamic value-added	Strcat	Push Append	Append Appendchar Appendformat

F) intercept

Function	Char *	String	Cstring
Get part score	Subscripts	Substr	Left Mid Right Truncate

G) Remove

Function	Char *	String	Cstring
Remove partial values		Remove	Remove
Remove Blank Value	Removeblanks Note: This is provided by ATL. It is not a C function.	Remove_if	Trim Trimleft Trimrig

H) case-insensitive Conversion

Function	Char *	String	Cstring
Case sensitivity	_ Strlwr _ Strupr		Makelower Makeupper

I) conversion from other types

Function	Char *	String	Cstring
Convert to number	Atoi Atod Atof		Format
Convert to char *		C_str	Getbuffer Getbuffersetlen

J) Format

Function	Char *	String	Cstring
Format	Sprintf		Format

K) Get the length

Function	Char *	String	Cstring
Get Length	Strlen	Length	Getlength
Get size		Size	Getalloclength

L) null judgment

Function	Char *	String	Cstring
Judge whether it is empty	Determine whether = NULL or whether the first character is''	Empty	Isempty

M) redefinition size

Function	Char *	String	Cstring
Redefinition size	Realloc New	Resize	Getbuffersetlength

N) release resources

Function	Char *	String	Cstring
Release	Free Delete (Delete [])		Releasebuffer Releasebuffersetlength

(5) Security>

Cstring> string> char *;

(6) Flexibility

Cstring> string> char *;

(7) portability

Char * = string> cstring

(8) Implementation of conversion

1. Convert string to cstring
Cstring. Format ("% s", String. c_str ());

2. Convert Char to cstring
Cstring. Format ("% s", char *);

3. Char to string
String S (char *);

4. Convert string to char *
Char * P = string. c_str ();

5. Convert cstring to string
String S (cstring. getbuffer ());

6. String-> cstring
Cstring. Format ("% s", String. c_str ());
C_str () is indeed better than data.
7. cstring-> string
String S (cstring. getbuffer ());
Releasebuffer () is required after getbuffer (). Otherwise, no space occupied by the buffer is released.
8. There are three functions that can convert the content of a string to a character array and a C-string
1. Data (), returns a string array ""
2, c_str (), returns a string array ""
3, copy ()

9. Convert the character to an integer. You can use atoi, _ atoi64, or atol.
10. convert numbers to cstring variables. You can use the format function of cstring.

Cstring S;
Int I = 64;
S. Format ("% d", I)
The format function is very powerful and worth your research.

11. cstring to char *
Charpoint = strtest. getbuffer (strtest. getlength ());

12. cstring conversion char [100]

Char A [100];
Cstring STR ("aaaaaa ");
Strncpy (A, (lpctstr) STR, sizeof ());