# Strings #
`Whamm` has very basic support for strings; they are injected into the instrumented Wasm program
and are represented as the tuple: `(memory_address, length)`. Only static strings can be defined,
e.g. `"i'm a string"`, no dynamic string creation is supported (yet), e.g. `"i " + " am " + " groot`.
However, as a workaround, you can pull a string from a user library to get this functionality.
```
var a: str = "";
var b: str = "The quick brown fox";
// var c: string = null; // INVALID -- strings cannot be set to null
```
## Escapes ##
Strings can use the `\` character to escape some sequences including:
- `\n` newline
- `\t` tab
- `\"` double quote
- `\'` single quote
- `\\` backslash
- `\0` null byte
- `\x(HEX_DIGIT{2})` to insert hex
- `\u(HEX_DIGIT+)` to insert unicode
-
```
// encodes the string literal: "hello drop😀😀A"
report var s: str = "hello drop\u{1F600}😀\x41\n";
```
# Strings and Libraries #
Strings can be passed to / pulled from libraries through memory operations. To have
this work in your own libraries, you will have to expose functions to allocate/free
memory.
Write to a library:
```
use whamm_core;
wasm:opcode:drop:before {
// initialize the string to pass
var s: str = "hello world!";
var l: u32 = s.len();
// allocate the right number of bytes to store the string
var ptr: i32 = whamm_core.mem_alloc(l as i32);
// write the string to the target library's memory
write_str(memid(whamm_core), ptr, s);
// call a function in the library that uses the passed string
// (this just prints the string)
whamm_core.puts(ptr, l as i32);
// free the allocated memory
whamm_core.mem_free(ptr);
}
```
Pull from a library:
```
use alpha;
wasm:opcode:drop:before {
// allocate some space in memory to store the library's string
var MAX: i32 = 100;
var ptr: i32 = alpha.mem_alloc(MAX);
// write a string to memory, return the length of the string written
var l: i32 = alpha.write_alphabet(ptr, MAX);
// read the string from the library's memory
var s: str = read_str(memid(alpha), ptr, l as u32);
// free the memory we've just used
alpha.mem_free(ptr);
}
```