Algorithms and Me: Strings : Remove duplicates from a string

A string is a collection of characters terminated by a special character '\0'. String can have duplicate characters in it. Today's problem requires purging of those duplicate characters from string and return the string.
Key Point: char[256],hashtable
From Coding Interviews: Questions, Analysis & Solutions
void DeletedDuplication(char* pString) {
    int hashTable[256];
    char* pSlow = pString;
    char* pFast = pString;

    if(pString == NULL)
        return;

    memset(hashTable, 0, sizeof(hashTable));

    while (*pFast != '\0') {
        *pSlow = *pFast;

        if(hashTable[*pFast] == 0) {
            ++ pSlow;
            hashTable[*pFast] = 1;
        }

        ++pFast;
    }

    *pSlow = '\0';
}
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