如何在C中检查临时文件？

问题描述

我刚刚编写了一个C程序（Ubuntu平台，使用GCC作为编译器），其中我有很大的内存，所有内存中都填充有有意义的数据：

u_char* bigChunkOfMem = populateData();       // This works
int memSize = sizeOfChunk( bigChunkOfMem );   // This also works

麻烦的是，我需要将此数据提交给另一个我未编写的函数。此函数将文件描述符作为输入，因此我需要将数据复制到临时文件中：

FILE* myTmpFile = tmpfile();

printf("Now copying contents of bigChunkOfMem into myTmpFile!\n");
int i=0;
while( i < memSize ){
    fputc( bigChunkOfMem[i],myTmpFile );
    printf("...just copied bigChunkOfMem[%d]:%u\n",i,bigChunkOfMem[i]);
    i++;
}
printf("\n");
rewind( myTmpFile );

我猜这在起作用...？我的输出是这样的：

Now copying contents of bigChunkOfMem into myTmpFile!
...just copied bigChunkOfMem[0]:101
...just copied bigChunkOfMem[1]:102
...just copied bigChunkOfMem[2]:103
...and so on...

但是，当然，我将myTmpFile提交给其他函数，但没有任何反应。另一个功能是不处理我的数据。

很可能我的数据格式错误。但是，暂时将其搁置一旁。在我的疑难解答中，确实让我感到困扰的是，在创建临时文件后，我没有办法检查它。我尝试使用fread（）：

char[200] buffer;
fread( buffer,memSize+1,1,myTmpFile );
printf("buffer is:: %s\n",buffer);
rewind( myTmpFile );

但这似乎没有用。输出为：

buffer is:: [[not my data]]

我假定临时文件在逻辑上与写入磁盘的“常规”文件在逻辑上没有什么不同，即，我应该能够使用与其他文件相同的所有工具检查临时文件。这个对吗？在线文档暗示了这一点，但是我找不到任何可以证实这一点的资料。谢谢。

解决方法

请尝试下面的代码，以了解如何在C中检查临时文件？

#include <windows.h>
#include <tchar.h>
#include <stdio.h>

#define BUFSIZE 1024

void PrintError(LPCTSTR errDesc);

int _tmain(int argc,TCHAR *argv[])
{
    HANDLE hFile     = INVALID_HANDLE_VALUE;
    HANDLE hTempFile = INVALID_HANDLE_VALUE; 

    BOOL fSuccess  = FALSE;
    DWORD dwRetVal = 0;
    UINT uRetVal   = 0;

    DWORD dwBytesRead    = 0;
    DWORD dwBytesWritten = 0; 

    TCHAR szTempFileName[MAX_PATH];  
    TCHAR lpTempPathBuffer[MAX_PATH];
    char  chBuffer[BUFSIZE]; 

    LPCTSTR errMsg;

    if(argc != 2)
    {
        _tprintf(TEXT("Usage: %s <file>\n"),argv[0]);
        return -1;
    }

    //  Opens the existing file. 
    hFile = CreateFile(argv[1],// file name 
                       GENERIC_READ,// open for reading 
                       0,// do not share 
                       NULL,// default security 
                       OPEN_EXISTING,// existing file only 
                       FILE_ATTRIBUTE_NORMAL,// normal file 
                       NULL);                 // no template 
    if (hFile == INVALID_HANDLE_VALUE) 
    { 
        PrintError(TEXT("First CreateFile failed"));
        return (1);
    } 

     //  Gets the temp path env string (no guarantee it's a valid path).
    dwRetVal = GetTempPath(MAX_PATH,// length of the buffer
                           lpTempPathBuffer); // buffer for path 
    if (dwRetVal > MAX_PATH || (dwRetVal == 0))
    {
        PrintError(TEXT("GetTempPath failed"));
        if (!CloseHandle(hFile))
        {
            PrintError(TEXT("CloseHandle(hFile) failed"));
            return (7);
        }
        return (2);
    }

    //  Generates a temporary file name. 
    uRetVal = GetTempFileName(lpTempPathBuffer,// directory for tmp files
                              TEXT("DEMO"),// temp file name prefix 
                              0,// create unique name 
                              szTempFileName);  // buffer for name 
    if (uRetVal == 0)
    {
        PrintError(TEXT("GetTempFileName failed"));
        if (!CloseHandle(hFile))
        {
            PrintError(TEXT("CloseHandle(hFile) failed"));
            return (7);
        }
        return (3);
    }

    //  Creates the new file to write to for the upper-case version.
    hTempFile = CreateFile((LPTSTR) szTempFileName,// file name 
                           GENERIC_WRITE,// open for write 
                           0,// do not share 
                           NULL,// default security 
                           CREATE_ALWAYS,// overwrite existing
                           FILE_ATTRIBUTE_NORMAL,// normal file 
                           NULL);                // no template 
    if (hTempFile == INVALID_HANDLE_VALUE) 
    { 
        PrintError(TEXT("Second CreateFile failed"));
        if (!CloseHandle(hFile))
        {
            PrintError(TEXT("CloseHandle(hFile) failed"));
            return (7);
        }
        return (4);
    } 

    //  Reads BUFSIZE blocks to the buffer and converts all characters in 
    //  the buffer to upper case,then writes the buffer to the temporary 
    //  file. 
    do 
    {
        if (ReadFile(hFile,chBuffer,BUFSIZE,&dwBytesRead,NULL)) 
        {
            //  Replaces lower case letters with upper case
            //  in place (using the same buffer). The return
            //  value is the number of replacements performed,//  which we aren't interested in for this demo.
            CharUpperBuffA(chBuffer,dwBytesRead); 

            fSuccess = WriteFile(hTempFile,dwBytesRead,&dwBytesWritten,NULL); 
            if (!fSuccess) 
            {
                PrintError(TEXT("WriteFile failed"));
                return (5);
            }
        } 
        else
        {
            PrintError(TEXT("ReadFile failed"));
            return (6);
        }
    //  Continues until the whole file is processed.
    } while (dwBytesRead == BUFSIZE); 

    //  The handles to the files are no longer needed,so
    //  they are closed prior to moving the new file.
    if (!CloseHandle(hFile)) 
    {
       PrintError(TEXT("CloseHandle(hFile) failed"));
       return (7);
    }
    
    if (!CloseHandle(hTempFile)) 
    {
       PrintError(TEXT("CloseHandle(hTempFile) failed"));
       return (8);
    }

    //  Moves the temporary file to the new text file,allowing for differnt
    //  drive letters or volume names.
    fSuccess = MoveFileEx(szTempFileName,TEXT("AllCaps.txt"),MOVEFILE_REPLACE_EXISTING | MOVEFILE_COPY_ALLOWED);
    if (!fSuccess)
    { 
        PrintError(TEXT("MoveFileEx failed"));
        return (9);
    }
    else 
        _tprintf(TEXT("All-caps version of %s written to AllCaps.txt\n"),argv[1]);
    return (0);
}

//  ErrorMessage support function.
//  Retrieves the system error message for the GetLastError() code.
//  Note: caller must use LocalFree() on the returned LPCTSTR buffer.
LPCTSTR ErrorMessage(DWORD error) 
{ 
    LPVOID lpMsgBuf;

    FormatMessage(FORMAT_MESSAGE_ALLOCATE_BUFFER 
                   | FORMAT_MESSAGE_FROM_SYSTEM 
                   | FORMAT_MESSAGE_IGNORE_INSERTS,NULL,error,MAKELANGID(LANG_NEUTRAL,SUBLANG_DEFAULT),(LPTSTR) &lpMsgBuf,NULL);

    return((LPCTSTR)lpMsgBuf);
}

//  PrintError support function.
//  Simple wrapper function for error output.
void PrintError(LPCTSTR errDesc)
{
        LPCTSTR errMsg = ErrorMessage(GetLastError());
        _tprintf(TEXT("\n** ERROR ** %s: %s\n"),errDesc,errMsg);
        LocalFree((LPVOID)errMsg);
}

我希望这段代码对您有用。

谢谢。

,

对于它的价值，我意识到我可以像检查其他文件一样检查tmp文件。打开并阅读。以下是适用于from here的代码：

void readTmpFile( FILE* f ){
        u_char * buffer = 0;
        long length;
        //FILE * f = fopen (filename,"rb");

        if (f) {
                fseek (f,SEEK_END);
                length = ftell (f);
                fseek (f,SEEK_SET);
                buffer = malloc (length);
                int dontcare = 0;
                if (buffer){
                        dontcare = fread (buffer,1,length,f);
                }
        fclose (f);
        }

        printPCAP_RAW( buffer,1 );

        free( buffer );
}