Question

What's wrong with my code? I just want to append a single space to the beginning of my string :( http://ideone.com/3EXbA

Answer 1

http://ideone.com/34snU

Answer 2

well when I take away the 'free' it works http://ideone.com/ZSzuO

Answer 3

but I want to get rid of the original string, or at least reuse it

Answer 4

I'm sure there is a much better way to do this...

Answer 5

I think your error is on line 21:
unsigned int len_engs = strlen(engs) + 1;

you are not taking into account the null character ('\0') that appears at the end of every C string. So you need to allocate "strlen(engs)+2" characters.

Answer 6

nah I took care of that in the malloc part

Answer 7

len_engs is the length of the characters, plus 1 for the nul character

Answer 8

so in malloc, I also add +1 to the len_engs to make space for the space

Answer 9

but you are padding it with an extra space, so you need another character

Answer 10

which is why I've added +1 to the len_engs when calling malloc

Answer 11

1 more byte for the space

Answer 12

oh - sorry - I didn't read ahead to the malloc part. let me re-read the code.

Answer 13

yeah I think the real trouble in my code is at the very end :)

Answer 14

why are you "free"ing at line 29?

Answer 15

I want to delete the original string

Answer 16

but the original string is allocated on the stack

Answer 17

right: the original string may not be malloc()ed so there's my problem :(

Answer 18

what do I do?

Answer 19

you need to define the responsibility of your function. if it is expected to be called only with malloc'ed strings then you cannot call it with a string allocated on the stack.
it is generally not good practice to write code like this - which is why I don't use C anymore and instead use C++ where you can make use of constructors/destructors, smart pointers, etc to manage memory in a much cleaner way.

Answer 20

:( right... this would be easier and cleaner if I used some other way of implementing strings.

Answer 21

but I wrote my program with this function in mind for accepting user input as strings: http://ideone.com/SUnx0

Answer 22

but I could rewrite padstring in a much cleaner way :-D

Answer 23

http://ideone.com/s4eTr

Answer 24

yes - strncpy makes it cleaner, but I still don't like writing functions that malloc. the problem you run into is who is responsible for freeing this memory? do you HAVE to code in C or can you use some other language like C++ or Java?

Answer 25

maybe you can rewrite it much better than I could :-D

Answer 26

I want to eliminate free()ing responsibility from everybody except the calling function which will be a big procedure that just translates an integer into an english sentence. Also I want to use C :-D

Answer 27

last time I coded in C was more than 20 years ago :-D

Answer 28

the only thing I could suggest here is that line 29 could be simplified further to:
strcpy(tempengs + 1, engs);
since "engs" is null terminated and you have allocated enough space to receive it in tempengs.

Answer 29

sorry line 28 not 29

Answer 30

alright this is what my code looks like now: http://ideone.com/I62Ka

Answer 31

but I think I should change fprintf(stdout.... ) to fprintf(stderr)

Answer 32

what else can I do to improve my stuff?

Answer 33

I still don't think its a good idea to free the original string in this method - it feels like an unexpected "side-effect". I think it might be better to leave the responsibility of freeing memory to the caller.

Answer 34

good idea

Answer 35

ok - good luck - but I would strongly advise you to move to a higher level language like C++, Java, Scala, etc

Answer 36

or how about I just realloc the original string, and then make a new buffer, write a space to the beginning of the buffer, copy the string to the buffer, rewrite the string with the buffer, and just free the buffer without worrying about the original string?.

Answer 37

but that won't change a thing... :-P

Answer 38

I would just be doing the same thing!

Answer 39

hmmm - again feels like an unexpected side-effect and relies on the original string being malloc'ed

Answer 40

isn't there an easier way to append a space to a string in C? without having to bust my butt implementing strings as something other than ordinary C strings?

Answer 41

I'll just use Java

Answer 42

:-) there probably is a better way of doing this but I would expect it to still involve allocating memory somewhere.

Answer 43

In Java that whole thing is just something like " " + source

Answer 44

but probably behind the scenes in Java it's doing the same thing :-D

Answer 45

exactly - you should use a language that makes it easy for you to express your ideas rather than it getting in the way of what you want to do.

Answer 46

creating a new string object and returning it :-D

Answer 47

all languages eventually get compiled down to the same bits. you need (should) pick a language that makes it as natural as possible for you to express your ideas.

Answer 48

right

Answer 49

You might find this article useful: http://wilsonmar.com/1strings.htm
the first section is on "C String Safety"

Answer 50

thanks!