如何在Node.js侧打印以PVoidArray传入的结构体数组？

Got it, let's break this down step by step. Since you're working with ffi, ref, and your pre-compiled libfun.so library, and want to print struct array elements passed as a PVoidArray without defining a dedicated struct array type, here's how to start with accessing and printing myArray[0]:

Prerequisite: Mirror Your C Struct in Node.js #

First, you need to replicate your C struct from fun.h using ref — this lets Node.js correctly interpret the raw memory behind the void* pointers. For example, if your C struct looks like this:

// fun.h
typedef struct {
    int id;
    char name[20];
    double value;
} Data;

Your Node.js struct definition would be:

const ref = require('ref');
const ffi = require('ffi-napi'); // Use ffi-napi for better Node.js compatibility, or raw ffi if you prefer

// Define the struct matching your C Data type
const DataStruct = ref.types.Struct({
    id: ref.types.int,
    name: ref.types.char.array(20), // Match fixed-length char array from C
    value: ref.types.double
});
// Create a pointer type for your struct
const DataPointer = ref.refType(DataStruct);

Load Your Library and Access myArray[0] #

Assuming you've already loaded libfun.so and have access to the myArray (a PVoidArray, which is essentially a void** in C), here's how to extract and print the first element:

// Load your library (adjust function signatures to match your actual C exports)
const libfun = ffi.Library('./libfun.so', {
    // Example: if your C function accepts the PVoidArray and its length
    processMyArray: ['void', ['pointer', 'int']]
});

// Assume myArray is the PVoidArray you're working with (passed in or returned from a C function)
// Step 1: Read the first void* from the array (offset 0, since each pointer takes ref.sizeof.pointer bytes)
const firstVoidPtr = ref.readPointer(myArray, 0);

// Step 2: Cast the void* to your struct pointer type
const firstDataPtr = firstVoidPtr.cast(DataPointer);

// Step 3: Dereference the pointer to get the actual struct instance
const firstData = firstDataPtr.deref();

// Step 4: Print the struct fields (adjust based on your actual struct members)
console.log('First element in the PVoidArray:');
console.log(`ID: ${firstData.id}`);
// For fixed-length char arrays, convert to a JS string manually
console.log(`Name: ${ref.readCString(firstData.name, 0)}`);
console.log(`Value: ${firstData.value}`);

Key Notes to Remember #

• Memory Safety: If the PVoidArray or structs it points to are allocated in C, use cleanup functions from libfun.so to free memory and avoid leaks.
• Dynamic Strings: If your struct uses a char* (dynamic string) instead of a fixed array, you can directly access firstData.name as a JS string (ref handles CString conversion automatically).
• Accessing Later Elements: For myArray[1], increment the offset by ref.sizeof.pointer (e.g., ref.readPointer(myArray, ref.sizeof.pointer)).

内容的提问来源于stack exchange，提问作者user9078927