How to use Strings in Assembly Language?
A string in assembly language is a sequence of characters that is stored in contiguous memory locations. Strings are used to represent text data, such as names, addresses, and messages.
To declare a string in assembly language, the programmer uses the .ascii or .asciz directive. The directive specifies the characters of the string. The .ascii directive terminates the string with a null character ('\0'), while the .asciz directive does not.
In this example, myString is a null-terminated string that contains the text "Hello, Assembly!".
Access a character of a string
Once a string has been declared, the programmer can access the characters of the string using an index. The index is a number that identifies the position of the character in the string. The first character of the string has index 0, the second character has index 1, and so on.
To access a character of a string in assembly language, the programmer uses the square bracket () operator. For example, the following assembly instruction loads the character of the string my_string at index 0 into the register al:
Calculating String Length
To calculate the length of a string in assembly, you typically iterate through its characters until the null terminator is encountered. Here's an example using the ecx register to store the length:
In this code, the find_length loop increments the ecx register until it finds the null terminator, indicating the end of the string. The length of the string is then stored in the ecx register.
Printing a String
Printing a string in assembly often involves using system calls. Here's an example using the write system call to print the string:
In this code, the write system call is used to print the string to the standard output (STDOUT). The eax, ebx, edx, and ecx registers are used to specify the syscall number, file descriptor, length of the string, and the address of the string, respectively.
Iterate over the characters of a string
Assembly language programmers can also use loops to iterate over the characters of a string. For example, the following assembly instruction loop prints each character of the string my_string to the console:
Exiting the Program
Finally, after performing the necessary operations, you may want to exit the program. Here's an example using the exit system call:
The exit system call is used to terminate the program. The eax register contains the syscall number, and xor ebx, ebx sets the exit status to 0.Full Source:
Strings are represented as sequences of characters stored in contiguous memory locations, often terminated with a null character. String operations involve iterating through characters, calculating lengths, and using system calls for printing or other manipulations.