题目:
编写函数htoi(s),把由十六进制数字组成的字符串(包含可选的前缀0x或0X)转换为与之等价的整型值。字符串中允许包含的数字包括:0~9、a~f以及A~F。
自我解答:
编程思路:
首先函数定义为 int htoi(const char s[]),输入参数用const加以声明,防止在函数内部对其改动;其次返回值为int型,当输入字符串有效时,输出相应的转换值,有无效字符时返回-1并抛出异常;
#include <stdio.h> /* convert a hex string to digit */ int htoi(const char s[]) { int i = 0; int hex = 0; bool skipHeader = false; /* judge the header is 0x or 0x */ while(s[i] != '\0') { if(!skipHeader && s[0] == '0' && (s[1] == 'x' || s[1] == 'X')) { skipHeader = true; if(s[2] == '\0') /* no digit after 0x or 0x */ { printf("lack of digits after 0x or 0X\n"); hex = -1; break; } else { i = 2; /* skip header:0x or 0X */ continue; } } else { if(s[i] >= '0' && s[i] <= '9') { hex = hex * 16 + (s[i] - '0'); } else if(s[i] >= 'a' && s[i] <= 'f') { hex = hex * 16 + (s[i] - 'a' + 10); } else if(s[i] >= 'A' && s[i] <= 'F') { hex = hex * 16 + (s[i] - 'A' + 10); } else { printf("error: illegal input: %c\n", s[i]); return -1; } i++; } } if(s[0] == '\0') { printf("no input\n"); hex = -1; } return hex; } int main() { printf("0x%x\n", htoi("1234")); printf("0x%x\n", htoi("0x1234")); printf("0x%x\n", htoi("0")); printf("0x%x\n", htoi("0x0")); printf("0x%x\n", htoi("0x1234ab")); printf("0x%x\n", htoi("0x1234AF")); printf("0x%x\n", htoi("0x123456789")); printf("%d\n", htoi("0x")); printf("%d\n", htoi("0s")); printf("%d\n", htoi("0x120xab")); printf("%d\n", htoi("")); }
运行结果为:
0x1234 0x1234 0x0 0x0 0x1234ab 0x1234af 0x23456789 lack of digits after 0x or 0X -1 error: illegal input: s -1 error: illegal input: x -1 no input -1
程序中考虑了如下几种情况:
1. 有效数字包含除0~9 a~f A~F之外字符
2. 自动判断是否以0x或0X开头,以及0x或0X之后是否有数字
3. 空字符串的情况
未考虑数据超范围的情况,这种情况会自动截断
参考答案: