Implementation of some basic operation codes of string

Fixed length sequential storage

#define MAXLEN 255 //  Predefined maximum string length 
typedef struct
{
    
    char ch[MAXLEN];    //  Each component stores one character 
    int length;         //  The actual length of the string 
} SString;

substring

//  substring . use  sub  Return string  S  No  pos  The length from characters is len The string of 
bool SubString(SString &sub, SString S, int pos, int len)
{
    
    if((pos + len - 1) > S.length)          //  Substring range is out of bounds 
    {
    
        return false;
    }
    for(int i = pos; i < pos + len; pos++)
    {
    
        sub.ch[i - pos + 1] = S.ch[i]; 
    }
    sub.length = len;
    return true;
}

Comparison operation

//  Comparison string  S  And string  T  Size ; if  S > T, Return value greater than 0; if  S < T, Return value less than 0; if  S = T, The return value is equal to 0
bool StrCompare(SString S, SString T)
{
    
    for(int i = 1; i <= S.length && i <= T.length; i++)
    {
    
        if(S.ch[i] != T.ch[i])
        {
    
            return S.ch[i] - T.ch[i];
        }
    }
    return S.length - T.length;             //  If all the characters scanned are the same, the long string will be larger 
}

Positioning operation

//  location . If the main string  S  And string exist in  T  Substring with the same value , Then return to his main string  S  The first place in ; Otherwise, the function value is 0
bool Index(SString S, SString T)
{
    
    int i = 1, n = StrLength(S), m = StrLength(T);
    SString Sub;          //  Temporary substring 
    while(i < (n-m+1))
    {
    
        SubString(sub, S, i, m);
        if(StrCompare(S, T) != 0)
        {
    
            ++i;
        }
        else
        {
    
            return i;       //  Returns the position of the substring in the main string 
        }
    }
    return 0;               // S There is no and T Equal substrings 
}