c - 带有字符类的 fscanf

Question

假设我有一个文件dog.txt

The quick brown fox jumps over the lazy dog.

我可以像这样从文件中读取

# include <stdio.h>
int main(){
  char str[10];
  FILE *fp;
  fp = fopen("dog.txt", "r");
  fscanf(fp, "%[ABCDEFGHIJKLMNOPQRSTUVWXYZ]", str);
  printf("%s\n", str);
  return 0;
}

程序将输出T。但是，我可以使用 POSIX 字符类(例如 [:upper:] )，而不是列出所有字母吗？

Answer 1

不，没有可移植的方法来做到这一点。某些实现允许您使用像 %[A-Z] 这样的字符范围，但 C 标准并不能保证这一点。 C99 §7.19.6.2/12 关于 [ 转换说明符(添加了强调)是这样说的:

The conversion specifier includes all subsequent characters in the format string, up to and including the matching right bracket (]). The characters between the brackets (the scanlist) compose the scanset, unless the character after the left bracket is a circumflex (^), in which case the scanset contains all characters that do not appear in the scanlist between the circumflex and the right bracket. If the conversion specifier begins with [] or [^], the right bracket character is in the scanlist and the next following right bracket character is the matching right bracket that ends the specification; otherwise the first following right bracket character is the one that ends the specification. If a - character is in the scanlist and is not the first, nor the second where the first character is a ^, nor the last character, the behavior is implementation-defined.

POSIX.1-2008 description具有几乎相同的措辞(甚至在意外冲突的情况下遵循 ISO C 标准)，因此在使用 POSIX 系统时，在这种情况下没有额外的保证。