Thread: Execute code from a text file?

Hi,

I have coded a very simple save function for a little game I'm messing about with at the moment. The program just writes all the variables to a text file.

Say I have a "hitpoints" variable, written as:

Code:

int hp = 25;

This will be written to a text file when the save function is called, and will be written like so:

Code:

fprintf(file, "hp = %d;", hp);

This will be written as follows when in saved, text format:

Code:

hp = 25;

Note: 25 may not be the actual value of the variable when it is saved.

The reason I have written it to the text file this way is because I was hoping I would be able to "load" this straight back into the program and actually execute this line, thus reinitialising the value to what it was when the save function was called.

My problem is I don't know how to actually execute the lines inside the text file when the program is running.

Reading this text file back into the program is no problem at all, but I don't want it just printed out to the screen.

Can anyone help me out?

Thanks.

if you can read it back into the program with 'no problem at all', then it seems youve accomplished what you needed to do. we cant tell you what to do with this variable after it has been read from the saved file (because your the only one who knows what to do with it). maybe you want to extract only the numerical part and assign it to some hp variable? since you know the format of the line should be "hp = X;" where X is some integer number, you can extract a substring of this line. ie starting at position index after "= " and going up to the second last character ";" (last character being newline). the characters between this range would be the hp, that you use "atoi" function to convert this substring to an integer to store in your int hp variable.

if this isnt what your looking for please give more specifics.

There is no way to "execute" the lines from a text file. You need to associate the value to the correct variable by yourself.
Remember that when you compile your code, the compiler transforms all that nice-named variables on memory address.
hp means nothing to the compiled program except you implement this association (as nadroj suggested).

Hey guys,

Thanks for replying. I am going to try what you've suggested. I didn't think it would be so easy.

In a nutshell, what I want to do is read the values back into the variables from which they came to begin with. Since the variables are all initialised to values when the program starts, I needed a way of saving them.


Thanks again.

Thanks for all your replies.

The fscanf function is what I was looking for, thanks Salem!

Originally Posted by QuantumPete

That's not entirely true. With a buffer overflow you can execute arbitrary code, including stuff you read from a text file. Obviously that's not in any way a good programming technique, but yes, "theoretically" it is possible.

It's also "theoretically" possible that you can include a C compiler in your code to parse the lines and assign the values directly to memory locations, but only insane people would do that for such simple tasks.

The only practical way is to use scanf, fgets, fread or similar and assign directly.

Personally if I had a bunch of variables I wanted to save across program runs, I would store them in a structure, and dump that entire structure to disk with fwrite/sizeof, and then read them all back on startup with fread/sizeof. Note that this is only portable across compilers if you save/restore each variable seperately rather than all at once due to structure padding.