blocks|key|1378092|text|如果你真的想要，尽情享受：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1378093|import+ctypes
g+=+(ctypes.c_char*40000).from_address(0x561124456)|code-block|syntax|javascript|1378094|看起来很有趣。两种语言(套接字、RPC等)都有很好的套接字连接库，所以如果是针对某个大型项目，我会再考虑一下。|1378095|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|L|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

If you really want to, enjoy:

<pre><code>import ctypes
g = (ctypes.c_char*40000).from_address(0x561124456)
</code></pre>

Looks like segfault fun. There are good socket-connection libraries on both languages (sockets, RPC etc...), so I would think about this again if this is for some large project.

blocks|key|1420350|text|我碰巧在类似的问题上工作。我的python脚本加载.so库以从c%2B%2B+.so获取图像缓冲区地址。获得缓冲区地址后，我需要能够读取缓冲区中的每个字节。我使用"from_address“创建了一个列表对象：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1420351|imageBytes+=+list(c_ubyte+*+dataSize).from_address(pointer)|code-block|syntax|javascript|1420352|下面详细介绍了如何获取从c%2B%2B传递到pyth的内存地址，以及如何在Python端访问内存数据。在c%2B%2B代码frameprovider.cpp中：|1420353|dataPackPtr+=+new+DataPack();+

DataPack+*+getFrame(){
++++uint32_t+width+=+1920;
++++uint32_t+height+=+1208;
++++const+size_t+buffersize+=+width+*+height+*+4;//rgba,+each+color+is+one+byte
++++unsigned+char*+rgbaImage+=+(unsigned+char+*+)malloc(buffersize);
++++memset(rgbaImage,+0,+buffersize);+//+set+all+the+buffer+data+to+0.
++++dataPackPtr->width+=+width;
++++dataPackPtr->height+=+height;
++++dataPackPtr->buffersize+=+buffersize;
++++dataPackPtr->bufferPtr+=+rgbaImage;
++++return+dataPackPtr;
}

extern+"C"+{
++++DataPack*+getFrame_wrapper(){
++++++++return+getFrame();
++++}
}|1420354|我的python：|1420355|import+ctypes
import+binascii
lib+=+ctypes.cdll.LoadLibrary('/libpath/frameprovider.so')
print+vars(lib)

class+dataPack(ctypes.Structure):
++++_fields_+=+[("width",ctypes.c_int),
++++++++++++++++("height",ctypes.c_int),
++++++++++++++++("buffersize",ctypes.c_int),
++++++++++++++++("bufferAddress",+ctypes.c_void_p)]

lib.getFrame_wrapper.restype+=+ctypes.POINTER(dataPack)
data+=+lib.getFrame_wrapper()
print+"in+python+the+w=+",+data.contents.width,+"h=",data.contents.height
print+"the+buffersize=",data.contents.height
imageBytes+=+list(
(data.contents.buffersize+*+ctypes.c_ubyte).
+from_address(data.contents.bufferAddress))++++++++

print+"the+len+of+imageBytes+are+",+len(imageBytes)
print+imageBytes[data.contents.buffersize+-1]+#print+the+last+byte+in+the+buffer
print+"in+python,+the+hex+value+of+element+12+is+",+hex(imageBytes[12])|1420356|entityMap^0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|R|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|S|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|T|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|U|8|@]|9|@]|A|$]]|$1|M|3|N|5|D|7|V|8|@]|9|@]|A|$E|F]]|$1|O|3|-4|5|6|7|W|8|@]|9|@]|A|$]]]|P|$]]

I happened to work on the similar issue. My python script load .so library to get an image buffer address from c++ .so. After I got the buffer address, I need to be able to read each byte in the buffer. I used "from_address" to create a list object:

<pre><code>imageBytes = list(c_ubyte * dataSize).from_address(pointer)
</code></pre>

The following shows the details how to get memory address passed from c++ to pyth and how to access the memory data on python side too. In c++ code frameprovider.cpp:

<pre><code>dataPackPtr = new DataPack(); 

DataPack * getFrame(){
 uint32_t width = 1920;
 uint32_t height = 1208;
 const size_t buffersize = width * height * 4;//rgba, each color is one byte
 unsigned char* rgbaImage = (unsigned char * )malloc(buffersize);
 memset(rgbaImage, 0, buffersize); // set all the buffer data to 0.
 dataPackPtr-&gt;width = width;
 dataPackPtr-&gt;height = height;
 dataPackPtr-&gt;buffersize = buffersize;
 dataPackPtr-&gt;bufferPtr = rgbaImage;
 return dataPackPtr;
}

extern "C" {
 DataPack* getFrame_wrapper(){
 return getFrame();
 }
}
</code></pre>

My python:

<pre><code>import ctypes
import binascii
lib = ctypes.cdll.LoadLibrary('/libpath/frameprovider.so')
print vars(lib)

class dataPack(ctypes.Structure):
 _fields_ = [("width",ctypes.c_int),
 ("height",ctypes.c_int),
 ("buffersize",ctypes.c_int),
 ("bufferAddress", ctypes.c_void_p)]

lib.getFrame_wrapper.restype = ctypes.POINTER(dataPack)
data = lib.getFrame_wrapper()
print "in python the w= ", data.contents.width, "h=",data.contents.height
print "the buffersize=",data.contents.height
imageBytes = list(
(data.contents.buffersize * ctypes.c_ubyte).
 from_address(data.contents.bufferAddress)) 

print "the len of imageBytes are ", len(imageBytes)
print imageBytes[data.contents.buffersize -1] #print the last byte in the buffer
print "in python, the hex value of element 12 is ", hex(imageBytes[12])
</code></pre>

blocks|key|1420346|text|一旦我从C中获得了内存位置的指针，我发现"list(listSize+*+listDataType).from_address(memoryPointer)“创建了C内存的一个内部副本。如果内存中的数据量很大，Python使用内部复制创建list对象需要很长时间。为了避免内部复制，我在python中使用了ctypelib.as_array：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1420347|import+ctypes
import+binascii
import+numpy+as+np

myCfunslib.getData.restype+=+ctypes.c_void_p
#myCfunslib.getData.restype=ctypes.POINTER(ctypes.c_ubyte)#no+need+to+cast
dataSize+=+1092+*+1208
#call+the+c+function+to+get+the+data+memory+pointer
cMemoryPointer+=+myCfunslib.getData();
newpnt+=+ctypes.cast(cMemoryPointer,+ctypes.POINTER(ctypes.c_ubyte))
#+and+construct+an+array+using+this+data
DataBytes+=+np.ctypeslib.as_array(newpnt,+(dataSize,))+#no+internal+copy
print+"the+mid+byte+of+the+data+in+python+side+is+",+DataBytes[dataSize/2]|code-block|syntax|javascript|1420348|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Once I got a pointer of memory location from C, I found "list(listSize * listDataType).from_address(memoryPointer)" created a internal copy of C memeory. If the data in memory is huge, Python takes a long time to create a list object by using internal copy. To avoid internal copy, I used the ctypelib.as_array in python:

<pre><code>import ctypes
import binascii
import numpy as np

myCfunslib.getData.restype = ctypes.c_void_p
#myCfunslib.getData.restype=ctypes.POINTER(ctypes.c_ubyte)#no need to cast
dataSize = 1092 * 1208
#call the c function to get the data memory pointer
cMemoryPointer = myCfunslib.getData();
newpnt = ctypes.cast(cMemoryPointer, ctypes.POINTER(ctypes.c_ubyte))
# and construct an array using this data
DataBytes = np.ctypeslib.as_array(newpnt, (dataSize,)) #no internal copy
print "the mid byte of the data in python side is ", DataBytes[dataSize/2]
</code></pre>

I want to read in a Python script a number of bytes starting from a specific address. E.g., I want to read 40000 bytes starting from 0x561124456.

The pointer is given from a C# app. I want to use this method to pass data between the app and script. I've used a TCP socket via localhost, but I want to try this method also.

How can I do this?

How to read from pointer address in Python?

Python

我想在Python脚本中读取从特定地址开始的一些字节。例如，我想从0x561124456开始读取40000字节。指针来自C#应用程序。我想使用此方法在应用程序和脚本之间传递数据。我已经通过localhost使用了TCP套接字，但我也想尝试一下这种方法。我该怎么做呢？

问如何在Python中读取指针地址？
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