blocks|key|629716|text|下面的内容对你有帮助吗？如果它给你错误或者我误解了你的问题，请告诉我：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|629717|size+=
printer+=
timeout+=

data+=+(ctypes.c_ubyte+*+size)()+#+line+5

C56_api_printer_read(printer,+data,+size,+timeout)

#+manipulate+data+eg
data[3]+=+7

C56_api_printer_write(printer,+data,+size,+timeout)|code-block|syntax|javascript|629718|编辑：|629719|关于第5行:另请参阅http://docs.python.org/library/ctypes.html的15.17.1.13和15.17.1.20节。|offset|length|629720|(ctypes.c_ubyte+*+size)|629721|给出了一个构造长度大小的ctype数组的函数。然后，在这一行中，我不带参数地调用函数，导致初始化为零。|629722|entityMap|0|LINK|mutability|MUTABLE|url|http://docs.python.org/library/ctypes.html^0|0|0|0|A|16|0|0|0|0^^$0|@$1|2|3|4|5|6|7|Y|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|Z|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|10|8|@]|9|@]|A|$]]|$1|I|3|J|5|6|7|11|8|@]|9|@$K|12|L|13|1|14]]|A|$]]|$1|M|3|N|5|D|7|15|8|@]|9|@]|A|$E|F]]|$1|O|3|P|5|6|7|16|8|@]|9|@]|A|$]]|$1|Q|3|-4|5|6|7|17|8|@]|9|@]|A|$]]]|R|$S|$5|T|U|V|A|$W|X]]]]

Does the following help you? Please let me know if it gives you errors or I misunderstood your question:

<pre><code>size =
printer =
timeout =

data = (ctypes.c_ubyte * size)() # line 5

C56_api_printer_read(printer, data, size, timeout)

# manipulate data eg
data[3] = 7

C56_api_printer_write(printer, data, size, timeout)
</code></pre>

Edit:

About line 5: See also <a href="http://docs.python.org/library/ctypes.html" rel="noreferrer">http://docs.python.org/library/ctypes.html</a> sections 15.17.1.13 and 15.17.1.20.

<pre><code>(ctypes.c_ubyte * size)
</code></pre>

gives a function that constructs a ctypes array of length size. Then in this line I call the function with no arguments, causing initialization with zeros.

blocks|key|262452|text|好的，在Kyss的帮助下，我完成了这项工作。以下是我完成此问题的测试代码和结果：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|262453|我的test.c代码：|262454|#include+<stdio.h>
int+test(unsigned+char+*test,+int+size){
++++int+i;
++++for(i=0;i<size;i%2B%2B){
++++++++printf("item+%25d+in+test+=+%25d\n",i,+test[i]);
++++}+++
}
int+testout(unsigned+char+*test,+int+*size){
+++test[2]=237;
+++test[3]=12;
+++test[4]=222;
+++*size+=+5;
}
main+()+{
++++test("hello",+5);+
++++unsigned+char+hello[]+=+"hi";
++++int+size=0;
++++int+i;
++++testout(hello,&size);
++++for(i=0;i<size;i%2B%2B){
++++++++printf("item+%25d+in+hello+=+%25d\n",i,+hello[i]);
++++}+++
}|code-block|syntax|javascript|262455|我创建了一个main来测试我的c函数。下面是函数测试的输出：|262456|item+0+in+test+=+104
item+1+in+test+=+101
item+2+in+test+=+108
item+3+in+test+=+108
item+4+in+test+=+111
item+0+in+hello+=+104
item+1+in+hello+=+105
item+2+in+hello+=+237
item+3+in+hello+=+12
item+4+in+hello+=+222|262457|然后我为共享进行了编译，所以它可以在python中使用：|262458|gcc+-shared+-o+test.so+test.c|262459|下面是我在python代码中使用的代码：|262460|from+ctypes+import+*

lib+=+"test.so"
dll+=+cdll.LoadLibrary(lib)
testfunc+=+dll.test
print+"Testing+pointer+input"
size+=+c_int(5)
param1+=+(c_byte+*+5)()
param1[3]+=+235+
dll.test(param1,+size)
print+"Testing+pointer+output"
dll.testout.argtypes+=+[POINTER(c_ubyte),+POINTER(c_int)]
sizeout+=+c_int(0)
mem+=+(c_ubyte+*+20)()+
dll.testout(mem,+byref(sizeout))
print+"Sizeout+=+"+%2B+str(sizeout.value)
for+i+in+range(0,sizeout.value):
++++print+"Item+"+%2B+str(i)+%2B+"+=+"+%2B+str(mem[i])|262461|和输出：|262462|Testing+pointer+input
item+0+in+test+=+0
item+1+in+test+=+0
item+2+in+test+=+0
item+3+in+test+=+235
item+4+in+test+=+0
Testing+pointer+output
Sizeout+=+5
Item+0+=+0
Item+1+=+0
Item+2+=+237
Item+3+=+12
Item+4+=+222|262463|成功了！|262464|我现在唯一的问题是根据输出的大小动态调整c_ubyte数组的大小。我已经发布了一个关于这个问题的单独问题。|262465|谢谢你的帮助，凯斯！|262466|entityMap^0|0|0|0|0|0|0|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|16|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|17|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|18|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|19|8|@]|9|@]|A|$]]|$1|K|3|L|5|F|7|1A|8|@]|9|@]|A|$G|H]]|$1|M|3|N|5|6|7|1B|8|@]|9|@]|A|$]]|$1|O|3|P|5|F|7|1C|8|@]|9|@]|A|$G|H]]|$1|Q|3|R|5|6|7|1D|8|@]|9|@]|A|$]]|$1|S|3|T|5|F|7|1E|8|@]|9|@]|A|$G|H]]|$1|U|3|V|5|6|7|1F|8|@]|9|@]|A|$]]|$1|W|3|X|5|F|7|1G|8|@]|9|@]|A|$G|H]]|$1|Y|3|Z|5|6|7|1H|8|@]|9|@]|A|$]]|$1|10|3|11|5|6|7|1I|8|@]|9|@]|A|$]]|$1|12|3|13|5|6|7|1J|8|@]|9|@]|A|$]]|$1|14|3|-4|5|6|7|1K|8|@]|9|@]|A|$]]]|15|$]]

Ok, after help from Kyss I was able to finish this out. Here's my test code and result for completion to this problem:

My test.c code:

<pre><code>#include &lt;stdio.h&gt;
int test(unsigned char *test, int size){
 int i;
 for(i=0;i&lt;size;i++){
 printf("item %d in test = %d\n",i, test[i]);
 } 
}
int testout(unsigned char *test, int *size){
 test[2]=237;
 test[3]=12;
 test[4]=222;
 *size = 5;
}
main () {
 test("hello", 5); 
 unsigned char hello[] = "hi";
 int size=0;
 int i;
 testout(hello,&amp;size);
 for(i=0;i&lt;size;i++){
 printf("item %d in hello = %d\n",i, hello[i]);
 } 
}
</code></pre>

I created a main for testing my c function. Here's the output of the function test:

<pre><code>item 0 in test = 104
item 1 in test = 101
item 2 in test = 108
item 3 in test = 108
item 4 in test = 111
item 0 in hello = 104
item 1 in hello = 105
item 2 in hello = 237
item 3 in hello = 12
item 4 in hello = 222
</code></pre>

Then I compiled for shared, so it could be used from python:

<pre><code>gcc -shared -o test.so test.c
</code></pre>

And here's what I used for my python code:

<pre><code>from ctypes import *

lib = "test.so"
dll = cdll.LoadLibrary(lib)
testfunc = dll.test
print "Testing pointer input"
size = c_int(5)
param1 = (c_byte * 5)()
param1[3] = 235 
dll.test(param1, size)
print "Testing pointer output"
dll.testout.argtypes = [POINTER(c_ubyte), POINTER(c_int)]
sizeout = c_int(0)
mem = (c_ubyte * 20)() 
dll.testout(mem, byref(sizeout))
print "Sizeout = " + str(sizeout.value)
for i in range(0,sizeout.value):
 print "Item " + str(i) + " = " + str(mem[i])
</code></pre>

And the output:

<pre><code>Testing pointer input
item 0 in test = 0
item 1 in test = 0
item 2 in test = 0
item 3 in test = 235
item 4 in test = 0
Testing pointer output
Sizeout = 5
Item 0 = 0
Item 1 = 0
Item 2 = 237
Item 3 = 12
Item 4 = 222
</code></pre>

Works!

My only issue now resides with dynamic resizing of the c_ubyte array based on the size of the output. I have posted a separate question regarding that though.

Thanks for your help Kyss!

My first post so please take at easy. :) I'm a bit new to Python as well, but I like what I see so far. What I'm trying to do is access a c library that allows me to print to a receipt printer via Python. I'm creating a wrapper in Python using ctypes, and everything is going great, EXCEPT for two functions. Here our their prototypes:

<pre><code>int C56_api_printer_write(int printer, unsigned char * data, int size, unsigned long timeout_ms);
int C56_api_printer_read(int printer, unsigned char * data, int size, unsigned long timeout_ms);
</code></pre>

My issue is with writing to and reading from unsigned char pointers using ctypes. I have to read in a bitmap file in Python and pass the array to the write function, or in the case of read, I need to read that pointer in as an integer array.

I've been floundering on this one for the past few hours, so I was hoping an expert could help by posting a simple example of how this could be accomplished. 

Thank you!

Python ctype help: working with C unsigned char pointers

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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这是我的第一篇文章，所以请放心。:)我对Python也有点陌生，但我喜欢我目前所看到的。我要做的是访问一个c库，它允许我通过Python打印到收据打印机。我使用ctype在Python中创建了一个包装器，除了两个函数之外，一切都很顺利。下面是他们的原型：int C56_api_printer_write(int pri...

问Python ctype帮助:使用C无符号字符指针
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