LabVIEW 调用库函数生成字符串数组

Question

我需要将 C 代码连接到 LabVIEW，我的 C 函数需要返回一个二维字符串数组。我宁愿不被迫提前预先确定数组的大小。所以我想知道，使用什么是正确的数据格式（C 字符串指针数组的句柄？字符串句柄数组的句柄？），如何正确进行分配，以及使用数组参数或return 类型。为 Call Library Function Node 提供的对话框只支持数字类型的数组，所以我有点不知道如何构建它。

Answer 1

你需要 LabVIEW Code Interface Reference Manual 来解决这个问题。

您正在编写一个 C 函数，它将 return 二维字符串数组发送到 LabVIEW。这意味着您需要 returning LabVIEW 的数据结构并使用 LabVIEW 的内存分配器。在您的 C 文件中包含 "extcode.h"（LabVIEW 附带）。然后创建以下 C 代码：

#include "extcode.h"

struct String2DArrayBlock {
    int32 dimensionSize1;
    int32 dimensionSize2;
    LStrHandle stringArray[1]; // Yes, this is intentional. Do not use LStrHandle* because that syntax changes the memory allocation. Old-school C code. LabVIEW's own C++ code has wrappers for managing this with more type safety. 
};

typedef String2DArrayBlock** String2DArrayHandle;

MgErr GenerateMyStrings(String2DArrayHandle *ptrToHandle) {
    if (!ptrToHandle)
        return mgArgErr; // Gotta pass a location for us to allocate.

    if (*ptrToHandle) {
        // This handle is already allocated. I'm not going to walk you through all the code needed to deallocate.
        return mgArgErr;
    }

    const int32 dimSize1 = ComputeHeight(); // This is your function... whereever your data is coming from.
    const int32 dimSize2 = ComputeWidth(); // Same here. 

    const int32 numberOfElements = dimSize1 * dimSize2;

    if (numberOfElements == 0) {
        return mgNoErr; // Done. NULL means empty array, and the handle is already NULL.
    }

    // DSNewHClr allocates the block and flood fills it with all zeros.
    *ptrToHandle = (String2DArrayHandle)DSNewHClr(sizeof(String2DArrayBlock) + ((numberOfElements - 1) * sizeof(LStrHandle))); // -1 because the sizeof block has 1 element. 
    if (!*ptrToHandle)
        return mFullErr; // Out of memory

    (**ptrToHandle)->dimensionSize1 = dimSize1;
    (**ptrToHandle)->dimensionSize2 = dimSize2;

    LStrHandle *current = (**ptrToHandle)->stringArray;
    for (int32 i = 0; i < numberOfElements; ++i, ++current) {
        std::string myCurrentString = GetMyCurrentString(i); // You write this however you look up the individual strings.
        if (myCurrentString.empty())
            continue; // NULL means empty string
        *current = (LStrHandle)DSNewHClr(sizeof(LStr)); // Allocates a zero-length LStrHandle.
        if (!*current)
            return mFullErr; // The array will be partially filled, but it is in a safe state for early return.
        MgErr err = LStrPrintf(*current, (CStr)"%s", myCurrentString.c_str());
        if (err)
            return err; // The array will be partially filled, but it is in a safe state for early return.
    }

    return mgNoErr;
}

针对 LabVIEW 运行时间引擎 (lvrt.dll) 编译您的代码。

在您的 G 代码中，放置一个调用库节点，添加一个参数 "Adapt to type" 和 "Pointers to Handles"，并用一个空的二维数组连接它。你完成了。

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