有C的setfill()替代方法吗? [英] Is there any setfill() alternative for C?

问题描述

在C ++中:

int main()
{
    cout << setfill('#') << setw(10) << 5 << endl;

    return 0;
}

输出:

#########5

C是否有任何 setfill()替代方案?还是在C中无需手动创建字符串就可以做到这一点?

Is there any setfill() alternative for C? Or how to do this in C without manually creating the string?

推荐答案

不，没有直接的选择.

但是，如果您具有良好的 snprintf (其行为符合C99标准的描述)，则无需创建新字符串即可工作；仅创建2个临时 int s

But if you have a well-behaved snprintf (one that behaves as described by the C99 Standard), this works without creating a new string; creating only 2 temporary ints

#include <stdio.h>

int main(void) {
  int filler = '#'; /* setfill('#') */
  int width = 10;   /* setw(10)     */
  int target = 5;   /* 5            */

  /* ******** */
  int s = snprintf(NULL, 0, "%d", target);
  for (int i = 0; i < width - s; i++) {
    putchar(filler);
  }
  printf("%d\n", target);
  /* ******** */

  return 0;
}

---

运行版本为 ideone .

C99 Standard的 snprintf 和Windows _snprintf 之间的区别(感谢您的链接，Ben ):

Differences between the C99 Standard's snprintf and Windows _snprintf (thank you for the link, Ben):

• 原型: int snprintf(char *限制缓冲区，size_t n，const char *限制格式，...);
• 原型: int _snprintf(char * buffer，size_t n，const char * format，...);
• snprintf 最多写入(n-1)个字节和一个NUL
• _snprintf 最多写入(n)个字节，最后一个字节可以是NUL或其他字符
• snprintf 返回格式所需的字符数(可以大于 n )或 -1 (如果出现编码错误)
如果 n 对于字符串来说不大，则
• _snprintf 返回负值；否则，返回负数.或 n (如果尚未将NUL字节写入缓冲区).

• prototype: int snprintf(char *restrict buffer, size_t n, const char *restrict format, ...);
• prototype: int _snprintf(char *buffer, size_t n, const char *format, ...);
• snprintf writes no more than (n-1) bytes and a NUL
• _snprintf writes no more than (n) bytes, the last of which may be NUL or other character
• snprintf returns the number of characters needed for format (can be larger than n) or -1 in case of encoding error
• _snprintf returns a negative value if n is not large for the string; or n if a NUL byte hasn't been written to buffer.

您可以循环运行行为不正确的 _snprintf ，增加 n 直到找到正确的值

You can run the mis-behaving _snprintf in a loop, increasing n until you find the right value

/* absolutely not tested, written directly on SO text editor */
int i;
size_t rightvalue = 0;
char buffer[SOME_DEFAULT_VALUE];
do {
    if (sizeof buffer < rightvalue) /* OOPS, BIG BIG OOPS */;
    i = _snprintf(buffer, rightvalue, "%d", 42);
} while (i != rightvalue++);
/* rightvalue already has space for the terminating NUL */

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