Strings

Formal Definition

The strings are sequences of 8-bit ASCII characters enclosed within quotation marks.

Simplified Syntax

"This is a string"

reg [8*number_of_characters:1] string_variable;

Description

The string should be given in one line. Strings can contain special characters (Example 1).

Character

Meaning

\n

New line character

\t

Tab character

\\

\ character

\”

" character

\ddd

A character specified by octal digit

Table 24: Summary of special characters

String variables should be declared as reg type vectors (Example 2). Each character needs 8 bits.

If a string variable is used in an expression, it should be treated as an unsigned value. If the size of a string assigned to a string variable is smaller than the declared size of the variable, then it will be left-padded with zeros.

The null string "” should be treated same as "\0”.

Concatenations of string variables preserve left-padded zeros of these variables (Example 3).

Examples

Example 1

"\n This is the first line\n This is the second line"
"\t Line\t with\t tab\t characters"

Example 2

reg [8*12:1] message;

The message variable can contain 12 characters.

Example 3

reg [10*8:1] s1, s2;
s1 = "Verilog";
s2 = "-HDL";
{s1, s2} <> {"Verilog", "-HDL"}

These expressions are not equal because {s1, s2} has 0s between "Verilog” and "-HDL” and {"Verilog”, "-HDL”} does not have any 0s between words.

Important Notes

  • Concatenation of string variables preserves left-padded zeros of these variables.

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