MQL4 Reference Language Basics Data Types Integer Types Character Constants

Character Constants

Characters as elements of a string in MQL4 are indexes in the Unicode character set. They are hexadecimal values that can be cast into integers, and that can be manipulated by integer operations like addition and subtraction.

Any single character in quotation marks or a hexadecimal ASCII code of a character as '\x10' is a character constant and is of ushort type. For example, a record of '0' type is a numerical value 30, that corresponds to the index of zero in the table of characters.

Example:

void OnStart()
  {
//--- define character constants
   int symbol_0='0';
   int symbol_9=symbol_0+9; // get symbol '9'
//--- output values of constants
   printf("In a decimal form: symbol_0 = %d,  symbol_9 = %d",symbol_0,symbol_9);
   printf("In a hexadecimal form: symbol_0 = 0x%x,  symbol_9 = 0x%x",symbol_0,symbol_9);
//--- enter constants into a string
   string test="";
   StringSetCharacter(test,0,symbol_0);
   StringSetCharacter(test,1,symbol_9);
//--- this is what they look like in a string
   Print(test);
  }

A backslash is a control character for a compiler when dealing with constant strings and character constants in a source text of a program. Some symbols, for example a single quote ('), double quotes ("), backslash (\) and control characters can be represented as a combination of symbols that start with a backslash (\), according to the below table:

Character name	Mnemonic code or image	Record in MQL4	Numeric value
new line (line feed)	LF	'\n'	10
horizontal tab	HT	'\t'	9
carriage return	CR	'\r'	13
backslash	\	'\\'	92
single quote	'	'\''	39
double quote	"	'\"'	34
hexadecimal code	hhhh	'\xhhhh'	1 to 4 hexadecimal characters
decimal code	d	'\d'	decimal number from 0 to 65535

If a backslash is followed by a character other than those described above, result is undefined.

Example

void OnStart()
  {
//--- declare character constants
   int a='A';
   int b='$';
   int c='©';      // code 0xA9
   int d='\xAE';   // code of the symbol ®
//--- output print constants
   Print(a,b,c,d);
//--- add a character to the string
   string test="";
   StringSetCharacter(test,0,a);
   Print(test);
//--- replace a character in a string
   StringSetCharacter(test,0,b);
   Print(test);
//--- replace a character in a string
   StringSetCharacter(test,0,c);
   Print(test);
//--- replace a character in a string
   StringSetCharacter(test,0,d);
   Print(test);
//--- represent characters as a number
   int a1=65;
   int b1=36;
   int c1=169;
   int d1=174;
//--- add a character to the string
   StringSetCharacter(test,1,a1);
   Print(test);
//--- add a character to the string
   StringSetCharacter(test,1,b1);
   Print(test);
//--- add a character to the string
   StringSetCharacter(test,1,c1);
   Print(test);
//--- add a character to the string
   StringSetCharacter(test,1,d1);
   Print(test);
  }

As it was mentioned above, the value of a character constant (or variable) is an index in the table of characters. Index being an integer, it can be written in different ways.

void OnStart()
  {
//---
   int a=0xAE;     // the code of ® corresponds to the '\xAE' literal
   int b=0x24;     // the code of $ corresponds to the '\x24' literal
   int c=0xA9;     // the code of © corresponds to the '\xA9' literal
   int d=0x263A;   // the code of ☺ corresponds to the '\x263A' literal
//--- show values
   Print(a,b,c,d);
//--- add a character to the string
   string test="";
   StringSetCharacter(test,0,a);
   Print(test);
//--- replace a character in a string
   StringSetCharacter(test,0,b);
   Print(test);
//--- replace a character in a string
   StringSetCharacter(test,0,c);
   Print(test);
//--- replace a character in a string
   StringSetCharacter(test,0,d);
   Print(test);
//--- codes of suits
   int a1=0x2660;
   int b1=0x2661;
   int c1=0x2662;
   int d1=0x2663;
//--- add a character of spades
   StringSetCharacter(test,1,a1);
   Print(test);
//--- add a character of hearts
   StringSetCharacter(test,2,b1);
   Print(test);
//--- add a character of diamonds
   StringSetCharacter(test,3,c1);
   Print(test);
//--- add a character of clubs
   StringSetCharacter(test,4,d1);
   Print(test);
//--- Example of character literals in a string
   test="Queen\x2660Ace\x2662";
   printf("%s",test);
  }

The internal representation of a character literal is the ushort type. Character constants can accept values from 0 to 65535.