c - 在我输入负整数之前，如何让这段代码扫描一个整数序列？我以为 %u 不会取负整数

Question

我希望 while 循环在我输入未签名的数字时结束(低于零)，但直到我输入一些符号才会发生在我的键盘上(字母等)然后调试停止。谁能帮忙我，好吗？

#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>

#define ALLOC_CHECK(p) if (!(p)) puts("Neuspesna alokacija"), exit(1)

bool is_palindrome(unsigned x)
{
    unsigned i, j, n = 8 * sizeof x; // Broj bita unsigned x

    for (i = 1 << n-1, j = 1; i > j; i >>= 1, j <<= 1)
        if (!(x & i) != !(x & j)) // Proverava da li su biti logicki razliciti
            return false;

    return true;
}

int main(void)
{
    unsigned size = 10, n = 0, i;
    unsigned *a = malloc(size * sizeof(*a));
    ALLOC_CHECK(a);

    puts("Enter a sequence of integers:");
    while (scanf("%u", &a[n++]))
        if (n == size) {
            size *= 2;
            a = realloc(a, size * sizeof(*a));
            ALLOC_CHECK(a);
        }

    // Moze i da se skrati na pravu duzinu sa a = realloc(a, n * sizeof(*a));

    puts("Binary palindromes are:");
    for (i = 0; i < n; i++)
        if (is_palindrome(a[i]))
            printf("%u ", a[i]);

    free(a);
}

Answer 1

I want that while loop ends when I enter number that's not unsigned (lower than zero).

将输入视为需要测试的文本。

// input examples
"-12345678901234567890" should stop the loop
"-1" should stop the loop
"123" should be read successfully as an `unsigned`
"  +123" should be read successfully as an `unsigned`
"12345678901234567890" is outside `unsigned` range and results are TBD
"abc" is not `unsigned`, so should stop loop.
"" is not `unsigned`, so should stop loop.
" 123 xyz"  is not `unsigned`, so should stop loop.
etc.

使用 fgets() 更健壮，但让我们尝试使用 scanf() 解决方案。

I thought %u won't take negative integers

scanf("%u",... 将接受像 "-123" 这样的输入并将其转换为 unsigned。所以需要代码来检测 -

以下将不会检测溢出或纯空白行，也不会在 - 之后消耗文本。

// consume leading white space, look for `-` (various approaches)
int n = 0;
scanf(" -%n", &n);
if (n > 0) exit_loop();  // `-` found

unsigned x;
if (scanf("%u", &x) != 1) exit_loop();  // non numeric input
// Success, use `x`
...

在使用 "%1[-]" 寻找 -

的 丑陋 while 循环中

char minus[2];
// while a search for `-` failed and `unsigned` succeeded 
while (scanf(" %1[-]", minus) != 1 && scanf("%u", &x) == 1) {
   ...
}