Programming in C:

In this problem, we will use our knowledge of strings to duplicate the functionality of the C standard library’s strtok() function, which extracts “tokens” from a string. The string is split using a set of delimiters, such as whitespace and punctuation. Each piece of the string, without its surrounding delimiters, is a token. The process of extracting a token can be split into two parts: finding the beginning of the token (the first character that is not a delimiter), and finding the end of the token (the next character that is a delimiter). The first call of strtok() looks like this:

char _∗ strtok(char _∗ str, const char _∗ delims);

The string str is the string to be tokenized, delims is a string containing all the single characters to use as delimiters (e.g. " \t"), and the return value is the first token in str. Additional tokens can be obtained by calling strtok() with NULL passed for the str argument:

char _∗ strtok(NULL, const char _∗ delims);

Because strtok() uses a static variable to store the pointer to the beginning of the next token, calls to strtok() for different strings cannot be interleaved. The code for strtok() is provided below:

char _∗ strtok ( char _∗ text , const char _∗ delims ) _{

/_∗ initialize _∗/

if (! text)

text = pnexttoken ;

/_∗ find start of token in text _∗/

text += strspn(text , delims);

if (_∗ text == ’\0’ )

return NULL;

/_∗ find end of token in text _∗/

pnexttoken = text + strcspn(text , delims);

/_∗ insert null₋terminator at end _∗/

if (_∗ pnexttoken != ’\0’ )

_∗ pnexttoken++ = ’\0’ ;return text ;

}

(a) In the context of our string tokenizer, the function strspn() computes the index of the first non-delimiter character in our string. Using pointers or array indexing (your choice), implement the strspn() function. In order to locate a character in another string, you may use the function strpos(), which is declared below:

int strpos ( const char str , const char ch );

∗

This function returns the index of the first occurrence of the character ch in the string str, or -1 if ch is not found. The declaration of strspn() is provided below:

unsigned int strspn( const char _∗ str , const char _∗ delims ) _{

/_∗ insert code here _∗/

}

Here, delims is a string containing the set of delimiters, and the return value is the index of the first non-delimiter character in the string str. For instance, strspn(" . This", " .") == 3. If the string contains only delimiters, strspn() should return the index of the null-terminator (’\0’). Assume ’\0’ is not a delimiter.

2

(b)The function strcspn() computes the index of the first delimiter character in our string.Here’s the declaration of strcspn():

unsigned int strcspn ( const char _∗ str , const char _∗ delims ) _{

/_∗ insert code here _∗/

}

If the string contains no delimiters, return the index of the null-terminator (’\0’). Implement this function using either pointers or array indexing.