CODEWITHSUNDEEP
carraysstring
Treborium
Treborium

Reputation: 23

C - Splitting C-String into words without reallocating memory

I'm trying to split a string (const char*) into words and saving the individual words in an array of char-pointer (char**).

My problem is not the splitting part but that I'm not allowed to allocate any memory. I need to use the input string as my memory, but since its a const char* I'm not able to modify it.

My thirst thought was to change all whitespaces into '\0' and save the position of the beginning of the words in the array, which of course is not possible since the input string is const.

The declaration of the function looks like this: 

int breakIntoWords(const char *line, int maxWords, char** words);

The function returns the number of words in line and maxWords is the size of the word-array.

Everything I found either used arrays as input strings or allocated memory with malloc.

Upvotes: 1

Views: 374

Answers (1)

John Bollinger
John Bollinger

Reputation: 181734

There is no solution to the problem as posed. You can obtain a pointer to the start of each word, but in order to use the source string as the storage for separate word strings you must modify it by replacing delimiters with string terminators, as you considered doing.

If the task indeed supposes that you will alter the input line to use it for storage of several separate strings, then it seems that it is inherently incorrect for the function's line parameter to be const-qualified. Such qualification is inconsistent with the job the function is supposed to perform. Moreover, if you are supposed to assign pointers into the string pointed to by line into words, then the fact that words is not const-qualified also presents a conflict.

The only plausible solution I see to the problem described is to remove the const qualifier from your line parameter.

Upvotes: 4

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