Save data in C and load it in Python [closed] - c

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I'm trying to produce a code in Python and I feed as an input a variable of a C program. How could I do this?
If the two codes where in Python I could use "pickle'' to store the information of the first one and then read it in the second one. But for what I've been reading there is not a pickle-like way to do it in C (please correct me if I am wrong, because I know almost nothing of C) and even if there exists such a way I'm unsure of the right way to "import'' it to Python.
The data I need to save is an "array of doubles'', that actually is a dynamic allocation of the memory.
BTW: What I'm doing now is get the print of the output, save it to a file and read it in python, but I'm losing decimal precision due the rounding when printing.

Answer 1

You can serialize the data in python using the struct.pack function, in C you can then unpack this information again using the union data type. I will give short codes in both languages on how to do both parts. The reverse is also possible and should be easy for you to do yourself should you require it. Remember that when you're sending doubles instead of floats you need to read 8 bytes in the C code each time.
In Python:
import struct
doublesArray = [5.0, 1.2, 3.4, 8.6]
file = open("transferdata", "wb")
for i in range(len(doublesArray)):
file.write(struct.pack('f', doublesArray[i]))
In C. By the way I took this code from this post:
#include <stdio.h>
#include <stdlib.h>
union
{
char asBytes[4];
float asFloat;
} converter;
int main(void)
{
FILE *fileptr;
char *buffer;
long filelen;
fileptr = fopen("transferdata", "rb");
fseek(fileptr, 0, SEEK_END);
filelen = ftell(fileptr);
rewind(fileptr);
buffer = (char *)malloc((filelen+1)*sizeof(char)); // Enough memory for file + \0
fread(buffer, filelen, 1, fileptr); // Read in the entire file
fclose(fileptr);
int i = 0;
while(i < filelen)
{
converter.asBytes[0] = buffer[i];
converter.asBytes[1] = buffer[i + 1];
converter.asBytes[2] = buffer[i + 2];
converter.asBytes[3] = buffer[i + 3];
i += 4;
char msg[32];
snprintf(msg, 32, "%f ", converter.asFloat);
printf(msg);
}
return 1;
}
[EDIT]: I see I wrote the exact opposite of what you need. I did not do that on purpose. However, I think you have enough information to figure out how to do the reverse on your own now.