通过引用将值从一个函数传递到另一个函数

Question

我需要一个从文件中读取数据块的程序。该块具有dwData和dwLength字段。 dwLength字段为sizeof dwData，就像字符串strlen一样。

此计划中的问题是readChunk0无法从dwLength初始化readChunk值。 dwLength中的readChunk值正常，因为cvar.mbsz消息正确显示（字符串的消息框）。

为什么我无法在测试功能中阅读dwLength？为什么dwData可以传递，dwLength。

//////////////////////////////////////////////////////////////
//  read contents of a chunk in dwData
//  and dwLength value in a hex file
//
//////////////////////////////////////////////////////////////
DWORD readChunk(DWORD dwData, DWORD dwLength, TCHAR ccSymbol[6]){
    HWND hWnd=cvar.get_hwnd();
    STRCK strform;//readChunk
    strform.cksize=sizeof(STRCK);
    //  strform.ccSymbol=
    //  strform.ckmaxsize=200;
    //  strform.nextck=0x4;

    //open file in HMMIO mode
    //filename is a common one
    cchmmio=mmioOpen("vocer.hex", NULL, MMIO_READ|MMIO_DENYNONE);
    if (cchmmio==NULL){
        MessageBox(hWnd, "eroare 1 mmioOpen", "titlu", 0);
        return 1;
    };

    MMCKINFO lpckParent={0,0,mmioFOURCC('W','A','V','E'),0,0};
    lpckParent.fccType=mmioFOURCC('W','A','V','E');
    lpckParent.cksize=sizeof(MMCKINFO)+sizeof(STRCK);
    HRESULT hr=mmioDescend(cchmmio, (LPMMCKINFO)&lpckParent, NULL, MMIO_FINDCHUNK);
    if ((hr!=MMSYSERR_NOERROR)&(hr!=MMIOERR_CHUNKNOTFOUND)){//&(hr!=MMIOERR_CHUNKNOTFOUND)){
        MessageBox(hWnd, "eroare 2", "titlu", 0);
        return 2;
    };
    if (hr==MMIOERR_CHUNKNOTFOUND){
        MessageBox(hWnd, "eroare 3 WAVE CHUNKNOTFOUND", "titlu", 0);
        return 3;
    };

    MMCKINFO mmckinfo;
    mmckinfo.ckid=mmioStringToFOURCC(ccSymbol, 0);
    //if you find the symbol, read dwData chunk;
    hr=mmioDescend(cchmmio, &mmckinfo, &lpckParent, MMIO_FINDCHUNK);
    if (hr==MMIOERR_CHUNKNOTFOUND){
        MessageBox(hWnd, "4) eroare fatala. ccSymbol not found", "titlu", 0);
        return 4;
    };

    if ((hr!=MMSYSERR_NOERROR)&(hr!=MMIOERR_CHUNKNOTFOUND)){
        MessageBox(hWnd, "eroare 5", "titlu", 0);
        return 5;
    }

    dwLength=(DWORD*)mmckinfo.cksize;
//  memcpy(&dwLength, &mmckinfo.cksize, 2);

    hr=mmioRead(cchmmio, (LPSTR)&dwData, (LONG)dwLength);
    if (hr!=(LONG)dwLength){
        MessageBox(hWnd, "eroare 6 mmioRead ccSymbol", "titlu", 0);
        return 6;
    };

    hr=mmioClose(cchmmio, 0);
    if (hr!=MMSYSERR_NOERROR){
        MessageBox(hWnd, "eroare 9 mmioClose", "titlu", 0);
        return 9;
    };

    //ok
    //  cvar.mbsz((LPSTR)dwData, "titlu", 0);//display dwData contents
    //  cvar.mbsz("strlen(szData):", "titlu", strlen((LPSTR)dwData));//display szData value
    cvar.mbsz("(DWORD)dwLength:", "titlu", (DWORD)dwLength);//display length read

    return 0;
}

// Test Function///////////////////////////////////////
//    open vocer.hex file
//    read a ccSymbol chunk and return the
//    dwData and dwLength values
//
void readChunk0(void){
    HWND hWnd=cvar.get_hwnd();
    DWORD dwData=(DWORD)calloc(200, sizeof(DWORD));
    DWORD dwLength=2;
    TCHAR cc[6]="x002";

    HRESULT    hr=readChunk((DWORD*)&dwData, (DWORD*)&dwLength, cc);
    if (hr){
        cvar.mbsz("eroare la revenirea din readChunk:", "titlu", hr);
        return;
    };
    //result is read in dwData
    //and has dwLength length

    //display the length of the message: dwLength (2 methods)
    //and contents of the dwData buffer
    TCHAR sztemp[256];
    sprintf(sztemp, "%d", dwLength);
    MessageBox(hWnd, sztemp, "titlu", 0);
    cvar.mbsz("(DWORD)dwlength:", "titlu", (DWORD)dwLength);
    MessageBox(hWnd, (LPSTR)dwData, "titlu:", 0);
}

修改的

感谢Diegos，感谢您的快速和良好的建议。我把它放在一起让你知道。

让我把它写下来，到目前为止我所理解的内容。

//////////////////////////////////////////////////////////////
//  read contents of a iData chunk and iLength value
//  in vocer.hex RIFF file
//
//////////////////////////////////////////////////////////////
DWORD readChunk(int* iData, int* iLength, LPSTR ccSymbol){
HWND hWnd=cvar.get_hwnd();

    if (!PathFileExists(szName0))
        strcpy(szName0, "vocer.hex");

    cchmmio=mmioOpen(szName0, NULL, MMIO_READ|MMIO_DENYNONE);

MMCKINFO lpckParent={0};
lpckParent.fccType=mmioFOURCC('W','A','V','E');
HRESULT hr=mmioDescend(cchmmio, (LPMMCKINFO)&lpckParent, NULL, MMIO_FINDCHUNK);
    if ((hr!=MMSYSERR_NOERROR)&(hr!=MMIOERR_CHUNKNOTFOUND)){
        MessageBox(hWnd, "eroare 2", "titlu", 0);
        return 2;
    };
    if (hr==MMIOERR_CHUNKNOTFOUND){
        MessageBox(hWnd, "eroare 3 WAVE CHUNKNOTFOUND", "titlu", 0);
        return 3;
    };

MMCKINFO mmckinfo={0};
    mmckinfo.ckid=mmioStringToFOURCC(ccSymbol, 0);
//daca ai gasit symbolul, citeste chunkul dwData;
    hr=mmioDescend(cchmmio, &mmckinfo, &lpckParent, MMIO_FINDCHUNK);
    if (hr==MMIOERR_CHUNKNOTFOUND){
        MessageBox(hWnd, "eroare 4. ccSymbol not found", "titlu", 0);
        return 4;
    };

    if ((hr!=MMSYSERR_NOERROR)&(hr!=MMIOERR_CHUNKNOTFOUND)){
        MessageBox(hWnd, "eroare 5", "titlu", 0);
        return 5;
    };

//  memcpy((int*)iLength, (long*)mmckinfo.cksize, 2);
    iLength[0]=mmckinfo.cksize;

TCHAR sztemp2[256];
TCHAR* sztemp=(TCHAR*)calloc(iLength[0]+1, sizeof(TCHAR));
    hr=mmioRead(cchmmio, (LPSTR)sztemp, (long)iLength[0]);
    sprintf(sztemp2, "iData:%s\nmmioRead:%d", (LPSTR)sztemp, hr);
    MessageBox(hWnd, (LPSTR)sztemp2, "titlu", 0);
    if (hr!=iLength[0]){
        cvar.mbsz("valoare dwLength:", "titlu", (long)iLength[0]);
        MessageBox(hWnd, "eroare 6 mmioRead ccSymbol", "titlu", 0);
        return 6;
    };

    for(int i=0; i<iLength[0]; i++)
        iData[i]=sztemp[i];
//      memcpy(&iData[i], &sztemp[i], 1);

    hr=mmioClose(cchmmio, 0);

    return 0;
}


//Functie Test//////////////////////////////////////////
//  open vocer.hex file
//  read ccSymbol chunk and return
//  dwData of dwLength
//
//////////////////////////////////////////////////////////////
void readChunk00(void){
HWND hWnd=cvar.get_hwnd();
int* iLength=(int*)calloc(1, sizeof(int));
int* iData=(int*)calloc(200, sizeof(int));
TCHAR ccSymbol[6]="0x02";
TCHAR sztemp[200];//=(TCHAR*)calloc(iLength[0]+2, sizeof(TCHAR));

HRESULT hr=readChunk((int*)iData, (int*)iLength, ccSymbol);

    wsprintf(sztemp, "dwLength:%d\niData:%s", iLength[0], (LPSTR)&iData[0]);
    MessageBox(hWnd, (LPSTR)sztemp, "titlu", 0);

    strcpy(sztemp, "");
    MessageBox(hWnd, "inainte de for", "titlu", 0);
    for(int i=0; i<iLength[0]; i++){
//      strcat(sztemp,(LPSTR)&iData[i]);
        sztemp[i]=(TCHAR)&iData[i];
    };

TCHAR* sztemp2=(TCHAR*)calloc(iLength[0]+2, sizeof(TCHAR));
    sprintf(sztemp2, "dwLength:%d\niData:%s", iLength[0], (LPSTR)sztemp);
//  sprintf(sztemp, "dwLength:%d\niData[1]:%d", iLength[0], iData[1]);
    MessageBox(hWnd, (LPSTR)sztemp2, "titlu", 0);
}


//Functie Test///////////////////////////////////////
//  deschide fisierul voce.hex
//  citeste un chunk ccSymbol si returneaza
//  dwData de dimensiune dwLength
//  metoda cu pointer
void readChunk0(void){
HWND hWnd=cvar.get_hwnd();
LPSTR ccSymbol="0x02";
int* dwLength=(int*)calloc(1, sizeof(int));

HGLOBAL hData=GlobalAlloc(GHND, (int)dwLength);
    if (hData==0){
        cvar.mbsz("eroare la GlobalAlloc:", "titlu", GetLastError());
        return;
    };

int* iData=(int*)GlobalLock(hData);
    if (iData==0){
        cvar.mbsz("eroare la GlobalLock:", "titlu", GetLastError());
        return;
    };

HRESULT hr=readChunk((int*)iData, (int*)dwLength, ccSymbol);
    if (hr){
        cvar.mbsz("eroare la revenirea din readChunk:", "titlu", hr);
        return;
    };

    hr=GlobalUnlock(hData);
    if (hr!=0){
        cvar.mbsz("eroare la GlobalUnlock:", "titlu", GetLastError());
        return;
    };

TCHAR* sztemp=(TCHAR*)calloc(dwLength[0]+2, sizeof(TCHAR));
    for(int i=0; i<dwLength[0]; i++)
        sztemp[i]=iData[i];

    strcat(sztemp, "\0");
    MessageBox(hWnd, (LPSTR)sztemp, "titlu", 0);
    cvar.mbsz("(DWORD)dwLength:", "titlu", dwLength[0]);

}

我设法让它最终运行。请指导下一次，因为calloc-function的实现方式与OS（WINDOWS XP）的GlobalAlloc相同。我写了两个具有相同结果的函数，如果我错了，请纠正我。函数测试readChunk00是用calloc完成的，它不能读取对readChunk中main函数完成的第一个参数dwLength [0]的修改。

函数readChunk0是为readChunk00创建的测试函数，但现在它使用GlobalAlloc＆amp;家庭功能，在我看来，操作系统可以更好地解释。

根据您的观点，calloc的第一个参数（dwLength [0]）是否通过调用hr = readChunk函数初始化不正确？这个主题并不重复。谢谢您的时间:)）

Answer 1

如果希望修改调用者看到的值，则需要将指向dwLength的指针传递给readChunk并在函数内取消引用它。

此外，鉴于dwData的初始化，其数据类型应为DWORD*。

---

编辑以了解新信息。

您的新aproach仍然存在一些问题。以下是我希望您可以整理的一些代码片段。

这是您应该声明readChunk功能的方式：

DWORD readChunk(DWORD* dwData, DWORD* dwLength, TCHAR ccSymbol[6])

在函数内部，这是您设置dwLength指向的值的方式：

*dwLength = mmckinfo.cksize;

在测试功能中，这是您声明dwData：

的方式

DWORD* dwData = calloc(200, sizeof(DWORD));

这就是你宣布dwLength：

的方式

DWORD dwLength;

最后，您将所有数据传递给readChunk：

HRESULT hr = readChunk(dwData, &dwLength, cc);

你真的需要熟悉指针的工作方式以及如何通过值传递参数或通过C中指针的间接传递。