How to correctly describe a pointer and a pointer to a pointer? #92
Comments
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Please format your text with markdown syntax, i can't read it friendly. If you want to create a pointer point to i32, just use |
Sorry. I corrected the formatting and tried to describe it in more detail |
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You can refer to other issues to realize how to call win API by ffi-rs |
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I advise you to figure out the parameters meaning of c. |
Without unwarp: Uncaught Error Error: expect External, got: Object |
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createPointer will return an array of pointer, you should use index 0 to get the pointer element. You can write it with typescript for type hints |
Yes, it compiles but doesn't work as expected: Output: 0 {} |
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Use restorePointer to restore the value in the pointer |
Final for LPDWORD. It works! Thank you. Output: 100 Question about this code: Should I free the pointer? Or should I clear the pointer only if in createPointer paramsType = DataType.External? Often in WinAPI we use NULL (nullptr) in parameters instead of a data pointer to indicate to WinAPI that we are not using this parameter. What is the best way to create NULL (nullptr)? |
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Use Use the code below to create null pointer |
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The most significant problem. I have greatly simplified the example and left only the essence of the problem. C++ // WinApi32.dll
// Allocate 100 chars (bytes) buffer and fill 99 chars with 'A', return POINTER to allocated buffer
void MemAlloc(char** ppBuffer)
{
*ppBuffer= (char*)::HeapAlloc(::GetProcessHeap(), HEAP_ZERO_MEMORY, 100); // Allocate 100 (bytes) buffer and save pointer
memset ((void*)*ppBuffer, 65 /* 'A' */, 99 ); // fill 99 chars with 'A'
}
// Free allocated buffer
void MemFree(char* pBuffer)
{
::HeapFree(::GetProcessHeap(), 0x00, pBuffer);
}
// C++ Usage
int main(void)
{
char* pBuffer = nullptr;
MemAlloc(&pBuffer);
printf("%s", pBuffer); // -> AAAAAAAAAAAAAAAAAAAAAAAAAAA....
MemFree(pBuffer);
return 0;
}JS I don't know how to correctly describe import. const winapi = define({
MemAlloc: {
library: WinApi32dll,
retType: DataType.Void,
paramsType: [ DataType.External]
},
MemFree: {
library: WinApi32dll,
retType: DataType.Void,
paramsType: [ DataType.External ]
}
})
winapi.MemAlloc(????);
winapi.MemFree(????);Sorry for my persistence but totally stuck at this point in code. |
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You can find the same type definition in test cases and call examples
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I looked at the code provided and did not find a solution. In your examples there is a size of the returned data, you create arrays based on this size or get ** in retType of DataType.External. |
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you can't restore an array without specify length safety，or you can restore it with a big size
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…------------------ Original ------------------
From: Ytd ***@***.***>
Date: Wed,Jan 22,2025 8:46 PM
To: zhangyuang/node-ffi-rs ***@***.***>
Cc: yuuang ***@***.***>, Comment ***@***.***>
Subject: Re: [zhangyuang/node-ffi-rs] How to correctly describe a pointer anda pointer to a pointer? (Issue #92)
You can find the same type definition in test cases and call examples
char** is a string array type
I looked at the code provided and did not find a solution.
In your examples there is a size of the returned data, you create arrays based on this size or get ** in retType of DataType.External.
In my case, the library returns a pointer to a buffer in a variable that I specified, in which I can find data, the size is not known to me and is not needed, since it will simply return a zero-terminated buffer to me.
char* pBuffer = nullptr; MemAlloc(&pBuffer); printf("%s", pBuffer); // -> AAAAAAAAAAAAAAAAAAAAAAAAAAA.... MemFree(pBuffer);`
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Let's do it differently, without text (char) data. The buffer will be a void type: void* pBuffer = nullptr;I want to get a pointer to it (it is allocated in C++) MemAlloc(&pBuffer);and I want to move through it until I find the first zero, outputting all the data to the console. At the end, I'll call flushing this buffer using C++. MemFree(pBuffer);How to get a direct pointer to allocated C++ memory on the heap? const voidPtr = createPointer({ paramsType: [DataType.RefVoid], paramsValue: [ 0 /* init value */ ] }); // <-- C++ void* pBuffer = nullptr;
let pVoid = unwrapPointer(voidPtr)[0]; // &pBuffer
winapi.MemAlloc(pVoid); // C++ MemAlloc(&pBuffer);
let text = Buffer.from(refPointer(voidPtr)[0], 0, 100 /* 100 for simplicity */) /* function not found in ffi-rs*/);
console.log(text.toString());
winapi.MemFree(pVoid); // C++ MemFree(pBuffer); |
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create DataType.u8array pointer with an enough size and fill it in c environment
发自我的iPhone
…------------------ Original ------------------
From: Ytd ***@***.***>
Date: Wed,Jan 22,2025 9:14 PM
To: zhangyuang/node-ffi-rs ***@***.***>
Cc: yuuang ***@***.***>, Comment ***@***.***>
Subject: Re: [zhangyuang/node-ffi-rs] How to correctly describe a pointer anda pointer to a pointer? (Issue #92)
you can't restore an array without specify length safety，or you can restore it with a big size
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…
Let's do it differently, without text (char) data.
The buffer will be a void type:
void* pBuffer = nullptr;
I want to get a pointer to it (it is allocated in C++)
MemAlloc(&pBuffer);
and I want to move through it until I find the first zero, outputting all the data to the console.
At the end, I'll call flushing this buffer using C++.
MemFree(pBuffer);
How to get a direct pointer to allocated C++ memory on the heap?
const voidPtr = createPointer({ paramsType: [DataType.RefVoid], paramsValue: [ 0 /* init value */ ] }); // <-- C++ void* pBuffer = nullptr; let pVoid = unwrapPointer(voidPtr)[0]; // &pBuffer winapi.MemAlloc(pVoid); // C++ MemAlloc(&pBuffer); let text = Buffer.from('ucs2', refPointer(voidPtr)[0] /* function not found in ffi-rs*/); console.log(text.toString()); winapi.MemFree(pVoid); // C++ MemFree(pBuffer);
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Do I understand correctly that your library cannot work with pointer to pointer as argument to functions in C++ ? func2(int **x);Example: void func1(int *);
void func2(int **);
int i = 100;
int *ptr = &i;
// when you want value of ptr should remain unchanged, but you want to change only value of i, use,
func1(int *)
// when you want value of ptr should change. i.e, it should point to some other memory other than i, use,
func2(int **); |
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Use |
Finally. My fully working version. In C++ everything works correctly. const voidPtr = createPointer({ paramsType: [DataType.Void], paramsValue: [ null ] }); // void* pBuffer = nullptr;
const stringPtr = wrapPointer(voidPtr)[0]; // &pBuffer
winapi.MemAlloc(stringPtr); // MemAlloc(&pBuffer)
console.log(restorePointer( { retType: [DataType.WString] , paramsValue: [ stringPtr ] } ), // printf('%s', (wchar*)pBuffer);
winapi.MemFree(stringPtr ); // MemFree(pBuffer);
freePointer({ paramsType: [DataType.Void], paramsValue: voidPtr, pointerType: PointerType.RsPointer } ); |
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The process crashes when I use freePointer. What is my mistake? // Process exited with code 3221226505 let ctxData = new Buffer.alloc(16).fill(0);
const ctxPtr = createPointer({ paramsType: [DataType.U8Array], paramsValue: [ ctxData] });
freePointer({ paramsType: [DataType.U8Array], paramsValue: ctxPtr, pointerType: PointerType.RsPointer } ); |
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Thank you, your code works, but I don’t understand what’s wrong with my version? |
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Use arrayConstructor to create array type instead of DataType.array |
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I guess this is my last question. You're probably already tired of me. My attempts are in JS but I don't understand if my approach is correct // ffi-rs type
const winapi = sqlconnectioninfoType : {
cbSize: DataType.I32,
szServerName : arrayConstructor({ type: DataType.U8Array, length: 261*2, ffiTypeTag: DataType.StackArray }),
szDataBaseName: arrayConstructor({ type: DataType.U8Array, length: 129*2, ffiTypeTag: DataType.StackArray }),
bIntegratedAuthentication : DataType.I32,
szLogin : arrayConstructor({ type: DataType.U8Array, length: 129*2, ffiTypeTag: DataType.StackArray }),
szPassword : arrayConstructor({ type: DataType.U8Array, length: 129*2, ffiTypeTag: DataType.StackArray })
}
// JS user data
const sqlconnectinfo = {
server: '(local)',
database: 'model',
intauth: false,
login : 'sqluser',
password: 'sqlpass'
};
// ffi-rs pointer
const _sqlconnectinfo_ptr = createPointer({ paramsType: [ winapi.sqlconnectioninfoType ], paramsValue: [ {
cbSize: winapi.sqlconnectioninfoSize.v1, /* i know size */
szServerName: Buffer.from(sqlconnectinfo.server + '\0', 'ucs2'),
szDataBaseName: Buffer.from(sqlconnectinfo.database + '\0', 'ucs2'),
bIntegratedAuthentication: sqlconnectinfo.intauth ? 1 : 0,
szLogin: Buffer.from(sqlconnectinfo.login + '\0', 'ucs2'),
szPassword: Buffer.from(sqlconnectinfo.password + '\0', 'ucs2')
}] });
// raw pointer
const _pSqlconnectinfo = unwrapPointer(_sqlconnectinfo_ptr)[0];
// Call
winapi.lib.SqlConnect(_pSqlconnectinfo );
freePointer({ paramsType: [winapi.sqlconnectioninfoType], paramsValue: _sqlconnectinfo_ptr, pointerType: PointerType.RsPointer }); |
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Support DataType.I16Array in [email protected] Use i16Array to represent |
If there is a way to initialize an array with default value? |
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Current ffi-rs version
Current Node.js arch
Descibe your problem in detail
I read the description of the library but could not call some WinAPI functions. Perhaps I didn't understand correctly how to use the library. I would really like you to explain it to me.
There are a couple of functions:
Pseudo example of Windows x32-x86 dll module:
How to call such functions correctly? I don't understand how to describe the parameters for
My implementation in Node
To describe the GUID in NODE I used this monster construction.
It works. Next, I convert it from binary to text form and everything is ok. Did I choose the right way or not?
For a pointer to a DWORD I can use a pointer to an Int32, but it doesn't work!
What would be the correct way to send NULL in WinAPI?
I can’t understand how to describe pointer to pointer
LPWSTR* -> char** - the most important parameter for both functions
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