String strings are a instance of System.String (or simplified to lowercase String) classes in C #, which represents a constant character sequence. The syntax created by the string is very simple: string s = "c # sharp XP", that is, the contents of the content as the string "C # Sharp XP" on the hosted stack, and S is only a reference handle to the memory area. Look at the following code: String S1 = "Hello, World!"; String S2 = S1; At this time, S1 and S2 point to the same block containing "Hello, World!" Memory area. C # provides two escape expressions for strings. The first type of escape character in traditional C / C is the same, that is, the expression of a counter-slope "/" plus atrical character. If "/ t" indicates the Tab key, "/ R" is represented by the carriage return, "/ n" means a wrap, etc. To indicate a file path under the C disk "My Document": string mypath = "c: // Documents and settings // cornfield // my documents // myfile.cs", where double slash is essential to single oblique line. The second representation method can be added to a "@" symbol before the string, so that the string can be expressed in the normal character sequence, as the above file path can be expressed like this: String mypath = @ "c : / Documents and settings / cornfield / my documents / myfile.cs ", the same as the previous expression. The second representation is useful in the case where we express a long string containing special characters, it can even express special characters such as enter-in-law, wrap, etc. You can get a single character in the string (16-bit Unicode encoding) in the string - this and the string array in C / C is essentially different. The following code demonstrates this: string s = "c # sharp XP"; for (int index = 0; index The following code example, the above-described method of the above method: use system; class test {spread s1 = "hello, world!"; String s2 = s1.clone (). TOSTRING (); / / Clon, handle, etc. = S3); // true, content equal console.writeline ((object) S1 == (Object) S2); // true, handle reference equal console.writeLine ((Object) S1 == (Object) S3); / / False, handle reference}} The constant meaning of the string constant string means that once the value of the string is created, it cannot be changed. Look at the typical code below: String S1 = "Hello,"; string s2 = "world!"; S1 = S2; After the above statement is executed, S1 is "Hello, World!", S2 is "World!". However, the original value "Hello" did not disappear, and "Hello" still has memory space, but now I can't be quoted by us, it can only wait for .NET's automatic garbage collector to recycle its resources. This causes memory leak in the previous C , which means that we will have "Hello, World!" (S1 reference handle points to the value), "World!" (S2 reference handle pointing Value), "Hello," (without a reference handle pointing this value) a total of three memory areas of the string. The character string value is also manifested on the parameter transmission as a string type, we look at the following example: use system; class test {public static void main () {string p = "hello,"; mymethod (p); console .Writeline (p); // Output "Hello,"} public static void mymethod (string p) {p = "world!"; Console.writeline (p); // Output hello, world!}} Although String type In C # is a reference type, but due to the constant nature of the string, the method MyMethod does not change the reference handle of the passed P (if you want to change, you need to use the REF keyword modification parameters), and this reference handle itself points to The memory area of the expression string "Hello" has not changed, and naturally, the calling string P through the MyMethod method will not change. Understanding the characteristics of the string value is very important to us in the C #, such as the System.String class, many ways do not change the string itself involved in the operation, but create a new value, just put the original The string is left to the auto garbage collector. If the string is frequent in the C # program, it is possible to cause a large number of "creation / discarding" actions, which must cause the system to make the system, and we should use the StringBuilder class.
