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PROGRAMMING => C / C++ /C# => Topic started by: Zeb on September 20, 2008

Title: [C] Making a substr function
Post by: Zeb on September 20, 2008

Since C has no feature to extract part of a string from a string (like PHP's substr does) I thought I'd modify an existing routine...

Code: [Select]

int substr(char **tFrom,int tTo,int tOffset, int tLen) {
  tTo = (char*) malloc(strlen(tFrom));
  strncpy(tTo, tFrom+2, 5);
  return tTo;
}
Any idea why this doesn't work?

Code: [Select]

  tTo = (char*) malloc(strlen(tFrom));
                                     ^
clparse.c(47) : Error: need explicit cast to convert
from: char *
to  : int
  strncpy(tTo, tFrom+2, 5);
                         ^
clparse.c(48) : Error: need explicit cast for function parameter 1 to get
from: int
to  : char *
--- errorlevel 1

Title: Re: [C] Making a substr function
Post by: hellfire on September 20, 2008

Code: [Select]

tTo = (char*) malloc(strlen(tFrom));here the input parameter "tTo" is an "int" but you assign a char* to it.

How about this?

Code: [Select]

char* substr(char *src, int start, int length)
{
  char *dst;
  if (length==0)
    length= strlen(src+start);
  dst = (char*) malloc(length+1);
  memcpy(dst, src+start, length);
  dst[length]=0;
  return dst;
}


Title: Re: [C] Making a substr function
Post by: Zeb on September 20, 2008

Thanks, that works!

How do you give karma?  Can't find the control!

This is where I get mega confused with C - where to use pointers/references/direct access to variables :/

Title: Re: [C] Making a substr function
Post by: Jim on September 21, 2008

You can't give out Karma until you reach 20 or 25 posts :)

Once you do get to grips with pointers you can see why C and C++ are amazing languages!

Jim

Title: Re: [C] Making a substr function
Post by: Zeb on September 21, 2008

The funny thing is, I already know what pointers are having coded assembler for about 10 years!

What I always found confusing is where to pass a pointer and when to pass the variable! I find C so confusing!

Title: Re: [C] Making a substr function
Post by: hellfire on September 21, 2008

Quote

having coded assembler

you'll notice that C is in many cases very near to assembly.
today there's not much reason to use only C (except of some embedded platforms).
In C++ you'll find that alot of these kind of things are already done.
Have a look at std::string (http://www.cplusplus.com/reference/string/string) for example...

Title: Re: [C] Making a substr function
Post by: Zeb on September 21, 2008

Thanks!

This book has [very] loosely covered variables and types, now I'm onto expressions and statements - can't wait until I hit the strings section as that's been my main cause for concern.

With assembler you can "see" exactly how a string is being handled/manipulated (especially with the help of MonAm) but C for me has been a little bit on the HELP I CAN'T FIGURE THIS OUT! side :D