SystemVerilog, a powerful hardware description language (HDL), offers robust string handling capabilities. Strings are sequences of characters enclosed in double quotes (“”). They are widely used in various applications, including testbench development, assertion-based verification, and configuration management.

String Declaration and Initialization

To declare a string variable, you can use the following syntax:

string str;

To initialize a string with a value, use the assignment operator:

str = "Hello, world!";

String Concatenation

You can concatenate strings using the + operator:

string str1 = "Hello";
string str2 = "World";
string str3 = str1 + " " + str2; // str3 will be "Hello World"

String Indexing and Slicing

You can access individual characters or substrings using indexing and slicing:

string str = "SystemVerilog";
// Access the first character
bit char1 = str[0]; // char1 will be 'S'
// Access a substring
string substr = str[3:6]; // substr will be "tem"

String Comparison

You can compare strings using the standard comparison operators:

string str1 = "Hello";
string str2 = "World";

if (str1 == str2) begin
    // Strings are equal
end else begin
    // Strings are not equal
end

String Functions

SystemVerilog provides several built-in functions for string manipulation:

• $strlen(str): Returns the length of the string str.
• $sscanf(str, format, ...): Parses a string according to a format string and assigns the parsed values to variables.
• $sprintf(str, format, ...): Formats data according to a format string and stores the result in the string str.
• $toupper(str): Converts all characters in the string str to uppercase.
• $tolower(str): Converts all characters in the string str to lowercase.

String in Testbenches

Strings are commonly used in testbenches to:

• Generate stimulus: Create complex test scenarios by generating input stimuli based on string patterns.
• Check responses: Verify output responses by comparing them with expected string values.
• Logging and reporting: Log messages and generate reports with detailed information.
• Configuration: Configure testbench parameters using string-based input files.