[英]Python ctypes: calling a function with custom types in c
I'm trying to wrap pre-existing c code for use in Python in Linux. 我正在尝试包装先前存在的C代码以在Linux中的Python中使用。 I have little experience with c, and I'm currently approaching this problem using ctypes.
我对c的经验很少,目前正在使用ctypes处理此问题。 My C function requires a 2d array with custom type entries and I don't know how to recreate this in python to pass it to the c function.
我的C函数需要带有自定义类型条目的2d数组,而且我不知道如何在python中重新创建此数组以将其传递给c函数。
Here is the function I'm attempting to call: 这是我尝试调用的函数:
void usbBuildGainTableAI_USB1808(libusb_device_handle *udev, Calibration_AIN table[NCHAN_1808][NGAINS_1808])
{
int i, j;
uint16_t address = 0x7000; // base address of ADC calibration coefficients.
for (i = 0; i < NCHAN_1808; i++) {
for (j = 0; j < NGAINS_1808; j++) {
usbMemAddressW_USB1808(udev, address);
usbMemoryR_USB1808(udev, (uint8_t *) &table[i][j].slope, sizeof(float));
address += 4;
usbMemAddressW_USB1808(udev, address);
usbMemoryR_USB1808(udev, (uint8_t *) &table[i][j].offset, sizeof(float));
address += 4;
}
}
return;
}
The header file has defined 头文件已定义
typedef struct Calibration_AIN_t {
float slope;
float offset;
} Calibration_AIN;
where NCHAN_18081 and NGAINS_1808 are constants and udev is an integer. 其中NCHAN_18081和NGAINS_1808是常量,而udev是整数。 I've followed an older question regarding multidimensional arrays and attempted to make a structure like the one in the c code.
我遵循了有关多维数组的一个较旧的问题 ,并试图在c代码中创建一种类似于多维数组的结构。
_1808 = CDLL(os.path.abspath("lib1808.so"))
NCHAN_1808 = 8 # max number of A/D channels in the device
NGAINS_1808 = 4 # max number of gain levels
class Calibration_AIN(Structure):
_fields_ = [("slope", c_float), ("offset", c_float)]
class AINarray(Structure):
_fields_ = [("array", (Calibration_AIN() * NCHAN_1808) * NGAINS_1808)]
table_AIN = AINarray()
_1808.usbBuildGainTableAI_USB1808(udev, table_AIN)
But there's a couple problems with this: the custom type Calibration_AIN can't be populated in an array with the operator * like an int or float can, and I can't pass a custom type through to c. 但这有两个问题:不能使用运算符*像int或float那样将自定义类型Calibration_AIN填充到数组中,并且我无法将自定义类型传递给c。 I've also tried making the array with a list of lists in Python, but I can't convert that to anything useful to c passable through ctypes.
我也尝试过使用Python中的列表列表来制作数组,但是我无法将其转换为对c可通过ctypes传递的任何有用信息。
How can I call this function from python without modifying the c code? 如何在不修改C代码的情况下从python调用此函数? Any help would be much appreciated, and also let me know if I should just learn c and try to write my program in c or Cython.
任何帮助将不胜感激,也请让我知道我是否应该学习c并尝试用c或Cython编写程序。 Ctypes may not be the best way of doing this.
Ctypes可能不是最好的方法。
The line: 该行:
_fields_ = [("array", (Calibration_AIN() * NCHAN_1808) * NGAINS_1808)]
should raise a TypeError , since you instantiate Calibration_AIN . 应该实例化 Calibration_AIN ,所以应该引发TypeError 。 I believe that what you meant was:
我相信您的意思是:
_fields_ = [("array", (Calibration_AIN * NCHAN_1808) * NGAINS_1808)]
But even so, you don't need the AINarray wrapper. 但是即使如此,您也不需要AINarray包装器。 According to [Python]: Arrays , you could do something like:
根据[Python]:Arrays ,您可以执行以下操作:
Calibration_AIN_Table = (Calibration_AIN * NCHAN_1808) * NGAINS_1808
and then, in order to initialize an instance do smth like: 然后,为了初始化实例,请执行以下命令:
>>> cat = Calibration_AIN_Table() >>> for i in range(NGAINS_1808): ... for j in range(NCHAN_1808): ... cat[i][j].slope = i * j ... cat[i][j].offset = i * i * j ... >>> cat[2][3].slope 6.0
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