C/C++ Programming Help Thread

[kuroneko]

I'm having problems with file i/o. I haven't had this problem before, and this code always worked fine until now:

      FILE* options;
      options = fopen("./files/options.txt","r+b");
      fseek(options, 0, SEEK_SET);
      fprintf(options, "s");
      fclose(options);

Looks fine to me (you can omit the fseek() though). To be sure I ran this on a completely different system and it does what you intended to do (i.e. replace the first character in the file with the letter 's').

Are you sure the file isn't read-only? Also, is options non-null as result of fopen()?

[Archaemic]

It would probably crash if options was null.

[Xsjado7]

The first answer is correct. If you want to store the second file's ten bytes after the first, you'd have to do:

sceIoRead(file2, buffer+10, 10);

Thanks, i was wondering how it worked

[Mr305]

Thanks, i was wondering how it worked

sceIoRead(file2, buffer+10, 10);
It work like this:

It writes to the initial pointer address of buffer + 10; pointer math.

[SuperBatXS]

Looks fine to me (you can omit the fseek() though). To be sure I ran this on a completely different system and it does what you intended to do (i.e. replace the first character in the file with the letter 's').

Are you sure the file isn't read-only? Also, is options non-null as result of fopen()?

No, it's obviously not a result of being null. However, i am opening and closing the file constantly in my program, but if i make a separate txt file for this code only (example - options2), then the code works flawlessly. So my guess is it's because i am opening and closing the file a lot? Can anyone explain this to me?

[Archaemic]

Note: ((int*)0x80000000) + 8 == (int*)0x80000020. It does not equal (int*)0x80000008, as one might expect. It increments the pointer by the sizeof what it points to.

[SuperBatXS]

Could someone help me out with this txt problem? Here is my FULL game code. Also, try to tell me how i optimize and remove unnecessary code.

http://rafb.net/p/LjnFOH38.html

[yaustar]

1. Indent your code properly so people can actually follow it: http://rafb.net/p/VCX2NU54.html
2. Just post the code with the problem, a ~1700 line single file isn't easy to follow.
3. Why not just open the file once, store the data and then refer to the data when you need it instead of opening the file again?
4. fprintf(options, "n"); actually puts 2 bytes into the file (strings are null terminated) not 1.

[SuperBatXS]

That's the way i always indent it (people have different styles). Lines 118-278, 1151-1156.

[eldiablov]

Im really not understanding the sceIoLseek command. The header gives a very brief description but I dont get it.

[yaustar]

I edited point 4 on my previous post:
4. fprintf(options, "n"); actually puts 2 bytes into the file (strings are null terminated) not 1.

People do have different styles but if you expect OTHER people to read it as well, you should use a STANDARD style such as ANSI or Kernighan & Ritchie or the very least, have a consistent style throughout the code submitted.

[Archaemic]

sceIoLseek is equivalent to fseek, except instead of returning success or failure, it returns the new position in the file. Use SEEK_CUR to seek from the current position, SEEK_SET to seek from the beginning of the file or SEEK_END to seek from the end of the file.

E] That PRNG (line 109) is broken.

rand_val = lo + rand_val % hi;

should be

rand_val = lo + (rand_val % (hi-lo));

E2]

Replace
fprintf(options, "1");
with
fputc('1',options);

[SuperBatXS]

I edited point 4 on my previous post:
4. fprintf(options, "n"); actually puts 2 bytes into the file (strings are null terminated) not 1.

People do have different styles but if you expect OTHER people to read it as well, you should use a STANDARD style such as ANSI or Kernighan & Ritchie or the very least, have a consistent style throughout the code submitted.

Sorry about the indents. :o
Do you have a link to a guide where i can learn this file i/o? Read and Write? I always have trouble with this.

[Archaemic]

I've revised my previous post. This, in addition to the reply to the PM I sent you, should fix up the problems you alluded to (in addition to fixing your PRNG)

[yaustar]

static int GetRandomNum(int lo, int hi)
{
    SceKernelUtilsMt19937Context ctx;
    sceKernelUtilsMt19937Init(&ctx, time(NULL)); //SEED TO TIME
    u32 rand_val = sceKernelUtilsMt19937UInt(&ctx);
    rand_val = lo + rand_val % hi;
    return (int)rand_val;
}

You should only seed the random number generator once, not everytime you want a random number.

[eldiablov]

So basically, the offset needed is just which number byte to start off from?

So if I want to start at the 800th byte I would just use the number 800?

[yaustar]

Sorry about the indents. :o
Do you have a link to a guide where i can learn this file i/o? Read and Write? I always have trouble with this.

http://www.cppreference.com/stdio/index.html in addition to the link IWN gave earlier to you.

Is what I normally use plus lots of experimentation and testing on the PC where I can debug more efficiently. Also, I personally prefer to use C++ file streams and ASCII text then C I/O and binary.

[SuperBatXS]

1) What is fputc? - nevermind, thanks for link yaustar
2) But i need the random number generator everytime i want a random number...

[yaustar]

SceKernelUtilsMt19937Context ctx;
    sceKernelUtilsMt19937Init(&ctx, time(NULL)); //SEED TO TIME

You perform this code once and store the context.

[SuperBatXS]

So what should i do to fix this problem?

[yaustar]

So what should i do to fix this problem?

Example:

static int GetRandomNum( SceKernelUtilsMt19937Context * pCtx, int lo, int hi)
{
    if( NULL == pCtx )
    {
        return 0;
    }
    int rand_val = (int)sceKernelUtilsMt19937UInt(pCtx);
    rand_val = lo + ( rand_val % (hi-lo) );
    return rand_val;
}

int main()
{
    SceKernelUtilsMt19937Context ctx;
    sceKernelUtilsMt19937Init(&ctx, time(NULL));
    
    // get random number
    GetRandomNum( &ctx, 0, 100 )
    
    return 0;
}

[SuperBatXS]

Yaustar, you smart, beastly, and ineffable genius......

I replaced fprintf with fputc, and i am getting a warning of being an incompatible pointer type.

[yaustar]

Can you post the full error and the block of code that produces it?

If you want to be even more clever with the GetRandomNum (and because it is in C), you can try this:

SceKernelUtilsMt19937Context InitialiseMtContext()
{
    SceKernelUtilsMt19937Context ctx;
    sceKernelUtilsMt19937Init(&ctx, time(NULL));

    return ctx;
}

int GetRandomNum(int lo, int hi)
{
    static SceKernelUtilsMt19937Context ctx = InitialiseMtContext();

    int rand_val = (int)sceKernelUtilsMt19937UInt(&ctx);
    rand_val = lo + ( rand_val % (hi-lo) );
    return rand_val;
}

int main()
{
    // get random number
    GetRandomNum( 0, 100 ); // ctx gets initialised here the first time the function is called
    GetRandomNum( 0, 100 ); // but not here
    GetRandomNum( 0, 100 ); // nor here

    return 0;
}

Please note, that if I was using C++, I wouldn't have written this code like this. I would use a class.

[SuperBatXS]

Error:

main.c(1379) : warning: passing argument 1 of 'fputc' makes integer from pointer
 without a cast
main.c(1379) : warning: passing argument 2 of 'fputc' from incompatible pointer
type

Block of code:

      FILE* options;
      options = fopen("./files/options.txt","r+b");
      fseek(options, 1, SEEK_SET);
      fputc(options, "1");
      fclose(options);

[yaustar]

fputc(options, "1");

Should be:

fputc(options, '1');

You were trying to pass a string instead of a char.

Also note, you need to do the same for your CPU settings as well.

[SuperBatXS]

This makes so much more sense....Thanks....:)

Edit:
Same error!

fputc(options, '1');

[Archaemic]

So basically, the offset needed is just which number byte to start off from?

So if I want to start at the 800th byte I would just use the number 800?

If you're using SEEK_SET and you start counting from 0, yes.

[SuperBatXS]

I'm still getting the same error Yaustar...

[yaustar]

http://www.cppreference.com/stdio/fputc.html

That is why. Look at the parameter order.

fputc('1', options);

[SuperBatXS]

I got it:
fputc('1', options);

Edit: Same time you posted i posted too (lol...):
http://www.mkssoftware.com/docs/man3/fputc.3.asp