c - 从用户那里读取号码

Question

这个问题已经有答案了:

Force input to be positive numbers only with error handling in C (3 个回答)

已关闭 8 年前。

我想从用户那里读取一个正整数。如果用户输入其他内容，我想再次询问。当用户输入负数时我就这样做了。但是如果用户输入一个字符或者其他什么，我该怎么办？

int main  (){   
    int takennumber;
    int number,multiplication,divisor,result,total=0;

    printf("Please,enter a integer number: ");
    scanf("%d",&takennumber);

    for(;takennumber<=0;)
    {
        printf("Wrong value! Please reenter: ");
        scanf("%d",&takennumber);
    }

Answer 1

如果您想完全控制输入处理(假设您只需要基数 10)，为什么不暴力破解它:

char buf[BUFSIZ], *p = buf;
char *retPtr;
unsigned long val;
Prompt();
while(fgets(buf, sizeof(buf)-1, stdin) {
    p = buf;
    while(isspace(*p)) p++);
    errno = 0; /* just in case errno isn't cleared in strtoul - may not be needed */
    /* strtoul used instead of strtol, to disallow negative number */
    val = strtoul(p, &retPtr, 10); /* 10 assumes base 10 only */
    /* strtoul returns value AND there no failure condition, we are good */
    if (errno == 0 || (val == LONG_MIN || val == LONG_MAX)) {
        /* See if anything follows the number on the line */
        if (*retPtr == '\n' || *retPtr == '\0') {
            break; // valid
        }
    }
    printf("Error message of your choice\n");
    Prompt();
}