expand函数

#include <stdio.h>void expand(char * s1, char * s2);int main(){return 0;}/*用strchr实现A-Z a-z的范围判定*/void expand(char * s1, char * s2) {/* 把'-' 和 非'-'作为 分类的标准*//* 其他不满足规则的字符都视为非法,判定出错信息 *//* 对于字符串前和字符串后的*/    static char upper_alph[27] = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";    static char lower_alph[27] = "abcdefghijklmnopqrstuvwxyz";    static char digits[11]     = "0123456789";        char * start, * end, * p;    int i = 0;    int j = 0;            /*  Loop through characters in s2  */        while ( s2[i] ) {        switch( s2[i] ) {        case '-':            if ( i == 0 || s2[i+1] == '\0' ) {                                /*  '-' is leading or trailing, so just copy it  */                                s1[j++] = '-';                ++i;                break;            }            else {                                 /*  We have a "range" to extrapolate. Test whether                     the two operands are part of the same range. If                     so, store pointers to the first and last characters                     in the range in start and end, respectively. If                      not, output and error message and skip this range.    */                                if ( (start = strchr(upper_alph, s2[i-1])) &&                     (end   = strchr(upper_alph, s2[i+1])) )                    ;                else if ( (start = strchr(lower_alph, s2[i-1])) &&                          (end   = strchr(lower_alph, s2[i+1])) )                    ;                else if ( (start = strchr(digits, s2[i-1])) &&                          (end   = strchr(digits, s2[i+1])) )                    ;                else {                                        /*  We have mismatched operands in the range,                        such as 'a-R', or '3-X', so output an error                        message, and just copy the range expression.  */                                        fprintf(stderr, "EX3_3: Mismatched operands '%c-%c'\n",                            s2[i-1], s2[i+1]);                    s1[j++] = s2[i-1];                    s1[j++] = s2[i++];                    break;                }                                                /*  Expand the range  */                                p = start;                while ( p != end ) {                    s1[j++] = *p;                    if ( end > start )                        ++p;                    else                        --p;                }                s1[j++] = *p;                i += 2;            }            break;                    default:            if ( s2[i+1] == '-' && s2[i+2] != '\0' ) {                                /*  This character is the first operand in                    a range, so just skip it - the range will                    be processed in the next iteration of                    the loop.                                   */                                ++i;            }            else {                                /*  Just a normal character, so copy it  */                                s1[j++] = s2[i++];            }            break;        }    }    s1[j] = s2[i];    /*  Don't forget the null character  */}