Since it's not possible to assign values to a const after it's initialized, how can I achieve this?
const double input1[1000][2];
for(int i = 0; i < 1000; i++){
input1[i][0] = i;
input1[i][1] = i*2;
}
3 Answers
You'll have to generate the explicit initialization (i.e. the { {0, 0}, {1, 2}, {2, 4}, ... etc etc ... {1000, 2000} }.
You can do this with map/apply macros, or with your build system - having it run some script which generates that initialization sequence and plants it into the file.
1 Comment
David Dominguez Herrera
Thank you. I'm going to try it!
You mentioned in the comments that this data is a training session data for a neural network.
I assume that you don't want to input 2000 values by hand and I assume that these values come from another file, perhaps a csv or the output of another program that generates the training data.
In that case, I'd write a script that generates a header file from the training data that looks like this:
// training_data.h
// trainng data, automatically generated by script gen_training_data.py
// do not modify this file
#ifndef TRAINING_DATA_H
#define TRAINING_DATA_H
const double traing_data[1000][2] = {
{ 0, 1 },
{ 0, 2 },
....
};
#endif
The script (that you can write with other languages, bash, python, perl) would take the training data and generate the header file for you, so you don't have to write 2000 values by hand. Then you can use it in your C program like this:
#include <stdio.h>
#include "training_data.h" // include auto generated file
int main(void)
{
...
feed_to_neural_network(training_data);
...
}
If you use a build system like cmake, you can let cmake execute your script so that it autogenerates the header file before compiling. That would save you on the long run a lot of time.
1 Comment
David Dominguez Herrera
This is what I needed! Thank you!
I don't understand why would you want to store the index value in the first index. But removing const can solve your issue. But better thing to do would be, to just store the value instead of index. Like following:
double input1[1000];
for (int i = 0; i < 1000; i++)
{
input1[i] = i * 2;
}
2 Comments
Billy
Hi Chux, i understand that assignment can't be done to a const object and hence i suggested in above answer to remove const. And also if you see the code i've suggested, it says
double and not const double.Billy
Since, he was looking to give specific value to an index (twice of index), it did not seem feasible or efficient way to initialize them all one by one. Hence i suggested to remove const and run a loop for assignment.
input1, user code can employiinstead ofinput1[i][0]andi*2instead ofinput1[i][1].constasconst, that makes no sense. If you want that yourconstarray is initialized with values, the you have to do it the hard wayconst double input1[1000][2] = { {0,1}, {0,2}, {0,3}, ... };const. Note thatconstis only a qualifier and you can always do something wrong with it, specially in c. Of courseconstwould protect you from accidentally doing something wrong, and I presume it would help the compiler optimize. But perhaps it's not worth it.