Cant allocate memory using MALLOC

Question

Can anyone help me as what is going wrong here? Am not able to allocate memory using malloc...

    bReadFile = ReadFile( hConsoleFile, &ReadFileBuffer, MaxCharToRead, &CharsRead, NULL );

We need more details-- are you getting a compile-time error (an error when you run the compiler) or a run-time error (an error when you run the program?) What is the text of the error message? — Max E., Feb 04 '12 at 06:17
I get a in my ReadFileBuffer...the file is just 35 chars which dwFileSize reads perfectly. — Abhineet, Feb 04 '12 at 06:18
malloc usually fails because it cant allocate enough memory. Set a breakpoint or print the value of dwFileSize and make sure you have enough Memory to allocate it. Try allocating a static amount and reading the file in chunks if the file is large. — Brad, Feb 04 '12 at 06:20
Actually it does not throws any error and successfully goes to the next method. But the ReadFileBuffer fails to read anything inside the File. Then I debugged it and saw the problem with ReadFileBuffer as . Is this the correct way to assign malloc for BYTE data types? — Abhineet, Feb 04 '12 at 06:22
I have set a breakpoint and saw the dwFileSize in debug mode that it reads perfectly the size of File. — Abhineet, Feb 04 '12 at 06:25

score 3 · Accepted Answer · answered Feb 04 '12 at 06:20

You have &ReadFileBuffer in the call to ReadFile. You are supposed to pass ReadFile a pointer to the buffer, not a pointer to a pointer to the buffer.

From the documentation:

lpBuffer [out]
    A pointer to the buffer that receives the data read from a file or device.

Since ReadFileBuffer is a pointer to the buffer, that's what you should be passing.

score 1 · Answer 2 · answered Feb 04 '12 at 06:23

The signature for ReadFile() is this:

BOOL WINAPI ReadFile(
  __in         HANDLE hFile,
  __out        LPVOID lpBuffer,
  __in         DWORD nNumberOfBytesToRead,
  __out_opt    LPDWORD lpNumberOfBytesRead,
  __inout_opt  LPOVERLAPPED lpOverlapped
);

The second parameter should be a pointer to your buffer, not a pointer to a pointer to your buffer. That's what you got when you did &ReadFileBuffer. The call should be:

bReadFile = ReadFile(hConsoleFile, ReadFileBuffer, MaxCharToRead, &CharsRead, NULL);

Cant allocate memory using MALLOC

2 Answers2