WebAssembly (WASM) for High Performance Apps · Aula

Troca básica de dados: tipos primitivos

Compreenda como passar tipos de dados simples, como inteiros e números de ponto flutuante, entre seu código JavaScript e WASM.

Troca básica de dados: tipos primitivos é uma aula grátis de WebAssembly (WASM) for High Performance Apps no CoddyKit. Esta é a aula 3 de 4. Você pode ler a aula completa abaixo gratuitamente — depois pratica ao vivo no navegador com um editor de código integrado e um tutor de IA 24/7. Faz parte do caminho de aprendizado de WebAssembly (WASM) for High Performance Apps, e seu progresso é sincronizado entre a web e o app CoddyKit. O curso de WebAssembly (WASM) for High Performance Apps inclui 4 aulas no total.

Partes desta aula ainda não foram traduzidas e aparecem em inglês.

Exchanging Basic Data Types

Welcome! In this lesson, we'll learn how to pass simple data types, known as primitives, between your JavaScript code and your WebAssembly (WASM) module compiled from C/C++.

Primitives include numbers like integers (int) and floating-point numbers (float, double). This is fundamental for enabling communication and interaction between your web application and high-performance WASM logic.

JS to WASM: Integer Input

Passing an integer from JavaScript to a C/C++ WASM function is quite direct. You define your C/C++ function with integer parameters, and Emscripten handles the necessary type mapping.

For example, a C function to add two integers would look like this:

int add_integers(int a, int b) {
  // Function body
  return a + b;
}

Example: WASM Integer Function

Let's look at a complete C program that defines a function to add two integers and exposes it to JavaScript using EMSCRIPTEN_KEEPALIVE.

Try running this code and see how it compiles:

#include <stdio.h>
#include <emscripten/emscripten.h>

#ifdef __cplusplus
extern "C" {
#endif

EMSCRIPTEN_KEEPALIVE
int add_integers(int a, int b) {
    printf("WASM: Adding %d and %d\n", a, b);
    return a + b;
}

#ifdef __cplusplus
}
#endif

int main() {
    printf("WASM module for integers loaded.\n");
    return 0;
}

Calling Integer Function from JS

After compiling the C code above, Emscripten generates a JavaScript glue code file (e.g., your_module.js) that provides access to your C functions.

You can then call the exported C function from your JavaScript code like this:

// Assuming 'Module' is the Emscripten-generated object
Module.onRuntimeInitialized = () => {
  // The C function is prefixed with an underscore by default
  const result = Module._add_integers(10, 25);
  console.log(`Sum from WASM: ${result}`); // Output: Sum from WASM: 35
};

WASM to JS: Integer Output

Returning an integer from a WASM function back to JavaScript is just as straightforward. C/C++ functions naturally return primitive types, and Emscripten ensures these return values are directly accessible in JavaScript.

Consider a C function that simply returns a fixed integer:

int get_magic_number() {
  return 42;
}

Example: WASM Returns Integer

Here's a C example that returns a specific integer. Notice the use of EMSCRIPTEN_KEEPALIVE to make it available to JavaScript.

Run this to see the simple C structure:

#include <stdio.h>
#include <emscripten/emscripten.h>

#ifdef __cplusplus
extern "C" {
#endif

EMSCRIPTEN_KEEPALIVE
int get_magic_number() {
    printf("WASM: Returning magic number.\n");
    return 42;
}

#ifdef __cplusplus
}
#endif

int main() {
    printf("WASM module for returning integers loaded.\n");
    return 0;
}

Exchanging Floating-Point Numbers

Passing floating-point numbers (float and double) between JavaScript and WASM works very similarly to integers. You define your C/C++ functions with float or double parameters and return types.

JavaScript's Number type is generally a 64-bit float (double-precision), which Emscripten automatically converts when passing to C/C++ float (32-bit) or double (64-bit) types.

Example: WASM Float Operations

Let's create a C function that takes two floats and returns their product, and another for doubles. This demonstrates both input and output of floating-point numbers.

Run this code to see how floats are handled:

#include <stdio.h>
#include <emscripten/emscripten.h>

#ifdef __cplusplus
extern "C" {
#endif

EMSCRIPTEN_KEEPALIVE
float multiply_floats(float a, float b) {
    printf("WASM: Multiplying floats %.2f * %.2f\n", a, b);
    return a * b;
}

EMSCRIPTEN_KEEPALIVE
double divide_doubles(double x, double y) {
    printf("WASM: Dividing doubles %.2f / %.2f\n", x, y);
    if (y == 0.0) return 0.0; // Avoid division by zero
    return x / y;
}

#ifdef __cplusplus
}
#endif

int main() {
    printf("WASM module for floats/doubles loaded.\n");
    return 0;
}

Type Matching is Key

While Emscripten handles much of the type conversion automatically, it's good practice to be aware of the underlying types:

JavaScript Number: This is typically a 64-bit floating-point number.
C/C++ int: Often 32-bit integer.
C/C++ float: 32-bit floating-point number.
C/C++ double: 64-bit floating-point number.

When passing a JS Number to a C float, there might be a slight loss of precision, as the 64-bit JS number is truncated to a 32-bit float.

Quick Check: Data Flow

You've learned how simple data types are exchanged. Let's test your understanding.

Recap: Primitive Exchange

Great job! You've mastered the basics of primitive data exchange between JavaScript and WebAssembly modules compiled from C/C++.

Simple data types like int, float, and double are straightforward to pass.
C/C++ functions can take them as parameters and return them as results.
Emscripten acts as the bridge, automatically converting between JavaScript's Number type and C/C++'s primitive types.
Be mindful of potential precision differences when converting between 64-bit (JS Number, C double) and 32-bit (C float, C int) types.

This fundamental understanding paves the way for exchanging more complex data structures later on!

Perguntas Frequentes

A aula “Troca básica de dados: tipos primitivos” é grátis?

Sim — o texto completo de “Troca básica de dados: tipos primitivos” é grátis para ler aqui na web. Para praticá-la interativamente (um editor de código integrado e um tutor de IA 24/7) e desbloquear o restante do curso de WebAssembly (WASM) for High Performance Apps, atualize para CoddyKit PRO. O curso de WebAssembly (WASM) for High Performance Apps inclui 4 aulas no total.

O que vou aprender em “Troca básica de dados: tipos primitivos”?

Compreenda como passar tipos de dados simples, como inteiros e números de ponto flutuante, entre seu código JavaScript e WASM. Você pratica WebAssembly (WASM) for High Performance Apps com código prático que executa diretamente no navegador, e um tutor de IA 24/7 responde suas dúvidas enquanto trabalha na aula.

Preciso ter experiência prévia para começar WebAssembly (WASM) for High Performance Apps?

Nenhuma experiência prévia é necessária. WebAssembly (WASM) for High Performance Apps no CoddyKit é estruturado para alunos iniciantes até avançados, então você pode começar aqui ou desde o início e aprender no seu ritmo. Esta é a aula 3 de 4.

Quanto tempo leva a aula “Troca básica de dados: tipos primitivos”?

A maioria das aulas CoddyKit leva cerca de 5–10 minutos. Cada uma é compacta e interativa, então você faz progresso constante e retoma exatamente de onde parou entre web e app.

Posso escrever e executar código nesta aula de WebAssembly (WASM) for High Performance Apps?

Sim. Cada aula de WebAssembly (WASM) for High Performance Apps inclui um editor de código integrado, então você escreve e executa código real direto no navegador e recebe feedback de IA instantaneamente — nenhuma configuração local necessária.

Todas as aulas deste curso

Compilando C/C++ para WASM com Emscripten
Carregando e executando WASM em JavaScript
Troca básica de dados: tipos primitivos
Chamando funções JavaScript a partir de C/C++

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