fopen - 不能写超过16K？ [英] fopen - can't write more than 16K?

问题描述

我目前使用fopen写/读二进制文件。小文件都是罚款。但在某些情况下，当确切的内容是> 16K文件的其余部分是无效的

I'm currently using fopen to write/read binary files. With small files all is fines. But in some cases, when "exactly" the content is > 16K the remainder of the file is invalid !!!

代码很简单，fopen ... fread / fwrite ... fflush ... fclose！

The code is simple, fopen ... fread/fwrite ... fflush ... fclose !

我试着用C ++。但现在我有一个问题，在读

I have try with C++. But now I got a problem during the "read"

在BinaryDefaultRead它返回-1！但真的不知道为什么！
我一次只写4个字节!!!

in BinaryDefaultRead it return -1 !!! But really don't know why ! I only write 4 bytes at a time !!!

它是在Win7 64位与MSVC 2008编译器。

It is under Win7 64 bits with MSVC 2008 compiler.

#include <fstream>

using namespace std;

size_t BinaryDefaultRead(ifstream& stream, void* buffer, unsigned int bufferSize)
{
    //return fread(buffer, 1, (size_t) bufferSize, file);
    stream.read((char*)buffer, bufferSize);
    if (!stream)
        return -1;

    return bufferSize;
}

size_t BinaryDefaultWrite(ofstream& stream, const void* buffer, unsigned int bufferSize)
{
    //return fwrite(buffer, 1, (size_t) bufferSize, file);
    stream.write((char*)buffer, bufferSize);
    if (!stream)
        return -1;

    return bufferSize;
}

// Read an unsigned integer from a stream in a machine endian independent manner (for portability).
size_t BinaryReadUINT(ifstream& stream, unsigned int* value)
{
    unsigned char buf[4];
    size_t result = BinaryDefaultRead(stream, (void *)buf, 4);

    if (result < 0)
        return result;

    *value = ((unsigned int) buf[0]) |
    (((unsigned int) buf[1]) << 8) |
    (((unsigned int) buf[2]) << 16) |
    (((unsigned int) buf[3]) << 24);

    return result;
}

// Write an unsigned integer to a stream in a machine endian independent manner (for portability).
size_t BinaryWriteUINT(ofstream& stream, unsigned int aValue)
{
    unsigned char buf[4];
    buf[0] = aValue & 0x000000ff;
    buf[1] = (aValue >> 8) & 0x000000ff;
    buf[2] = (aValue >> 16) & 0x000000ff;
    buf[3] = (aValue >> 24) & 0x000000ff;

    return BinaryDefaultWrite(stream, (void*)buf, 4);
}

// Read a floating point value from a stream in a machine endian independent manner (for portability).
size_t BinaryReadFLOAT(ifstream& stream, float* value)
{
    union {
        float f;
        unsigned int  i;
    } u;
    size_t result = BinaryReadUINT(stream, &u.i);

    if (result < 0)
        return result;

    *value = u.f;

    return result;
}

// Write a floating point value to a stream in a machine endian independent manner (for portability).
size_t BinaryWriteFLOAT(ofstream& stream, float aValue)
{
    union {
        float f;
        unsigned int  i;
    } u;
    u.f = aValue;
    return BinaryWriteUINT(stream, u.i);
}

size_t BinaryReadUINTArray(ifstream& stream, unsigned int* buffer, unsigned int count)
{
    size_t result;
    for(unsigned int i = 0; i < count; i++)
    {
        result = BinaryReadUINT(stream, buffer + i);
        if (result < 0)
            return result;
    }

    return result;
}

size_t BinaryWriteUINTArray(ofstream& stream, unsigned int* buffer, unsigned int count)
{
    size_t result;
    for(unsigned int i = 0; i < count; i++)
    {
        result = BinaryWriteUINT(stream, buffer[i]);
        if (result < 0)
            return result;
    }

    return result;
}

size_t BinaryReadFLOATArray(ifstream& stream, float* buffer, unsigned int count)
{
    size_t result;
    for(unsigned int i = 0; i < count; i++)
    {
        result = BinaryReadFLOAT(stream, buffer + i);
        if (result < 0)
            return result;
    }

    return result;
}

size_t BinaryWriteFLOATArray(ofstream& stream, float* buffer, unsigned int count)
{
    size_t result;
    for(unsigned int i = 0; i < count; i++)
    {
        result = BinaryWriteFLOAT(stream, buffer[i]);
        if (result < 0)
            return result;
    }

    return result;
}

推荐答案

fopen 只用于打开文件流，不能读或写。 fread 和 fwrite 用于执行此操作。

fopen is only used to open a file stream, not to read or write. fread and fwrite are used to do that.

fwrite 和 fread 不要确保写入所有传递的元素：它们返回写入的元素数

fwrite and fread don't ensure you to write all the elements you pass them: they return the number of elements written, which can be lesser than the number of elements you passed it.

只需检查返回的值，并保留 fwrite 直到你写出所有的元素或直到流有错误：使用 ferror 来检查错误。

Just check the returned value, and keep fwrite-ing until you write out all of your elements or until there's an error with the stream: use ferror to check for an error.

从 fwrite 手动：

fread（）和fwrite（）返回成功读取或写入的项目数（即不是字符数）。如果发生错误或达到文件结尾，返回值为短项目计数（或零）。

fread() and fwrite() return the number of items successfully read or written (i.e., not the number of characters). If an error occurs, or the end-of-file is reached, the return value is a short item count (or zero).

fread（）不区分文件结束和错误，调用者必须使用feof（3）和ferror（3）来确定发生了什么。

fread() does not distinguish between end-of-file and error, and callers must use feof(3) and ferror(3) to determine which occurred.

这篇关于fopen - 不能写超过16K？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！