[英]How to creating ctypes variables using python variables instead of hard-coded values?
When creating ctypes
variables, can one not pass values using python variables? 创建
ctypes
变量时,是否可以不使用python变量传递值?
I have some code where I am calling a shared C library. 我在调用共享C库的地方有一些代码。 If I pass the parameters to this C library using Method 1 (see below) things work well.
如果我使用方法1(参见下文)将参数传递给此C库,则一切正常。 But if I use Method 2, I get garbage.
但是,如果我使用方法2,则会得到垃圾。 There are other parts to the code.
该代码还有其他部分。 But I have confirmed that when I replace Method 2 with Method 1, things work well.
但是我已经确认,当我用方法1替换方法2时,一切正常。 So something is wrong here.
所以这里有些问题。
If what I am doing in Method 2 is not valid, what is the alternative if I want to automate the process of running the code for different values of a given variable(s)? 如果我在方法2中所做的操作无效,那么如果我想针对给定变量的不同值自动运行代码的过程,该怎么办?
Method 1 (This works well) 方法1(效果很好)
import ctypes as C
c_thresholds = (C.c_double * 4)()
for idx, value in enumerate(thresholds):
c_thresholds[idx] = value
goodH = Good(C.c_char('H'), C.c_double(0.5), C.c_int(100), C.c_int(20))
goodL = Good(C.c_char('L'), C.c_double(0.5), C.c_int(75), C.c_int(20))
c_parameters = Params(
var1 = C.c_int(100),
var2 = C.c_int(4),
var3 = C.c_int(5),
var4 = C.c_int(5000),
var5 = C.c_char_p("modelname"),
var6 = C.c_double(0.5),
var7 = C.c_double(90),
var8 = c_thresholds,
var9 = C.c_int(2),
H = goodH,
L = goodL
)
runsimulation(c_parameters)
Method 2 (This does not work, outputs garbage) 方法2(这不起作用,输出垃圾)
import ctypes as C
def create_cparams(var1, var2, var3, var4, var5, var6, var7, var8, var9):
c_thresholds = (C.c_double * 4)()
for idx, value in enumerate(var8):
c_thresholds[idx] = value
goodH = Good(C.c_char('H'), C.c_double(0.5), C.c_int(100), C.c_int(20))
goodL = Good(C.c_char('L'), C.c_double(0.5), C.c_int(75), C.c_int(20))
c_parameters = Params(
var1 = C.c_int(var1),
var2 = C.c_int(var2),
var3 = C.c_int(var3),
var4 = C.c_int(var4),
var5 = C.c_char_p(var5),
var6 = C.c_double(var6),
var7 = C.c_double(var7),
var8 = c_thresholds,
var9 = C.c_int(var9),
H = goodH,
L = goodL
)
return c_parameters
# These are python variables
var1 = 100
var2 = 4
var3 = 5
var4 = 5000
var5 = "modelname"
var6 = 0.5
var7 = 90
var8 = [1, 0.9, 0.8, 0.7]
var9 = 2
# Calling the create_cparams function defined above
c_parameters = create_cparams(var1, var2, var3, var4, var5, var6, var7, var8, var9)
runsimulation(c_parameters)
In case it is helpful the Params class is given by (does not change across the two methods): 如果有帮助的话,Params类是由给定的(在这两种方法中不变):
class Params(C.Structure):
_fields_ = [
("var1", C.c_int),
("var2", C.c_int),
("var3", C.c_int),
("var4", C.c_int),
("var5", C.c_char_p ),
("var6", C.c_double),
("var7", C.c_double),
("var8", (C.c_double * 4) ),
("var9", C.c_int),
("H", Good),
("L", Good)
]
C function prototype C函数原型
// runsimulation() function above calls this C function
void run_multiple_reps (struct params parameters, struct repdata *data,
int len_timepdsarr, int *timepdsarr)
// params struct on C side, which Params class duplicates
struct params
{
int var1;
int var2;
int var3;
int var4;
char *var5;
double var6;
double var7;
double var8[4];
int var9;
struct good H;
struct good L;
};
The field attributes of a Structure
are CField
descriptor objects. Structure
的字段属性是CField
描述符对象。 A descriptor is like a Python property
or like a __slots__
attribute, if you're familiar with either of those. 如果您熟悉描述符,则描述符就像Python
property
或__slots__
属性。 A CField
knows the data type of the field and its offset into the buffer. CField
知道字段的数据类型及其在缓冲区中的偏移量。 Each C data type has a associated get/set function that converts to and from Python objects. 每个C数据类型都有一个关联的get / set函数,该函数在Python对象之间来回转换。 So generally you can assign a Python object directly to the field.
因此,通常您可以将Python对象直接分配给该字段。 For example:
例如:
thresholds = [1, 0.9, 0.8, 0.7]
c_parameters = Params(
var1 = 100,
var2 = 4,
var3 = 5,
var4 = 5000,
var5 = "modelname",
var6 = 0.5,
var7 = 90,
var8 = (C.c_double * 4)(*thresholds),
var9 = 2,
H = Good('H', 0.5, 100, 20),
L = Good('L', 0.5, 75, 20),
)
If ctypes needs to hold a reference to a Python object to keep it alive, the reference is stored in the _objects
dict of the Structure
. 如果ctypes需要保留对Python对象的引用以使其保持活动状态,则该引用将存储在
Structure
的_objects
dict中。 In this case the array in var8
, for example, is simply copied into the buffer, so c_parameters
doesn't need to hold a reference to the original. 例如,在这种情况下,只需将
var8
的数组复制到缓冲区中,因此c_parameters
不需要保留对原始c_parameters
的引用。
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