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我有一个 C 程序，它从我的相机获取图像并将二进制数据写入文件。

我（迄今为止没有成功）试图编写一个python脚本来模仿C代码。

Python ctypes 示例似乎执行没有错误，直到我尝试将其写入文件。换句话说，在 Python 中，fwrite在这种情况下无法将数据写入文件。 fwrite返回 的值0，指示0文件已写入。

所以，我要问以下问题： 由于我有一个外部 c 函数正在读取二进制数据，大概是内存中的某个缓冲区，Python ctypes 的实例是否可能根本没有对该内存位置的读取访问权限？如果是这种情况，python ctypes 是否有可能获得访问内存中适当区域所需的权限？

作为参考，我包含了一个（按预期工作）简化的 C 示例，后面是下面的 Python ctypes 示例，它打开并创建了适当的文件，但不写入它。

//Data Saving Sample
//The sample will open the first camera attached
//and acquire 3 frames.  The 3 frames will be saved
//in a raw format and can be opened with applications
//such as image-j

#define NUM_FRAMES  3
#define NO_TIMEOUT  -1

#include "stdio.h"
#include "picam.h"
#include <iostream>
using namespace std;

int main()
{

    // The following structure contains the image data
    AvailableData data;

    int readoutstride = 2097152;
    FILE *pFile;


    Acquire( NUM_FRAMES, NO_TIMEOUT, &data, &errors );

    pFile = fopen( "sampleX3.raw", "wb" );
    if( pFile )
    {
        fwrite( data.initial_readout, 1, (NUM_FRAMES*readoutstride), pFile );
        fclose( pFile );
    }

}

这是我的 Python 版本：

""" Load the picam.dll """
picamDll = 'DLLs/Picam.dll'
picam = ctypes.cdll.LoadLibrary(picamDll)

libc = ctypes.cdll.msvcrt
fopen = libc.fopen

data = AvailableData()
readoutstride = ctypes.c_int(2097152)

"""
This is the C-structure form from the provided header file, followed by the Python syntax for creating the same structure type
typedef struct AvailableData
{
    void* initial_readout;
    int64 readout_count;
} AvailableData;

class AvailableData(ctypes.Structure):
    _fields_ = [("initial_readout", ctypes.c_void_p), ("readout_count",ctypes.c_int64)]
"""

"""
Simplified C-Prototype for Acquire

Acquire(
int64                       readout_count,
int                       readout_time_out,
AvailableData*         available);
"""
picam.Acquire.argtypes = int64, int, ctypes.POINTER(AvailableData)

picam.Acquire.restype = int

print picam.Acquire( 3, -1, ctypes.byref(data), ctypes.byref(errors))

""" Write contents of Data to binary file """
fopen.argtypes = ctypes.c_char_p, ctypes.c_char_p
fopen.restype = ctypes.c_void_p

fwrite = libc.fwrite
fwrite.argtypes = ctypes.c_void_p, ctypes.c_size_t, ctypes.c_size_t, ctypes.c_void_p
fwrite.restype = ctypes.c_int

fclose = libc.fclose
fclose.argtypes = ctypes.c_void_p,
fclose.restype = ctypes.c_int

fp = fopen('PythonBinOutput.raw', 'wb')
print 'fwrite returns: ',fwrite(data.initial_readout, 3*readoutstride.value, 1, fp)
fclose(fp)
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1 回答 1

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创建一个与常规 Python 文件一起使用的数组。例如：

获取一个空指针：

class AvailableData(Structure):
    _fields_ = [
        ("initial_readout", c_void_p), 
    ]

cglobals = CDLL(None) # POSIX dlopen
cglobals.malloc.restype = c_void_p

size = 100  # 3 * readoutstride.value
data = AvailableData(cglobals.malloc(size))

现在将其用作数组：

buf = (c_char * size).from_address(data.initial_readout)
with open('PythonBinOutput.raw', 'wb') as f: 
    f.write(buf)
于 2013-07-02T02:22:30.183 回答