将使用wscanf读取的宽字符串转换为C中的整数

Question

I am trying to convert a string read using wscanf to an integer using wcstol, both from header file wchar.h on Linux. While wcstol works on constant wide-char strings (eg L"23") it does not work on wscanf input, which puzzles me. I always get 0, even if the input is actually numeric (eg 23). Why?

$ ./test 
23
s=23
0

Here is my test program:

#include <stdio.h>
#include <wchar.h>
int main() {
  wchar_t s[100];
  if (wscanf(L"%s", s) == 1) {
    wprintf(L"s=%s\n", s);
    wprintf(L"%ld\n", wcstol(s, NULL, 10));
  }
}

If instead of wcstol I use strtol, it works but I get this warning:

/usr/include/stdlib.h:183:17: note: expected 'const char * restrict' but argument is of type 'wchar_t * {aka int *}'

which I could silent using a type cast. I thought wcstol was the right way to parse a wide-char string to an integer. Since on my machine chars are actually ints, strtol happens to work, but that leaves me still unsure whether this is the right solution. What's going on here? Why wcstol does not do its job?

Answer 1

Your problem is with the wscanf() format. A %s field descriptor designates a pointer to char , just like for scanf() . These two functions differ a bit in how they convert the input, but they agree on the meaning of the field descriptors.

For reading into an array of wchar_t , you want %ls . Moreover, whether you should use wscanf() of scanf() is primarily a function of how the input is encoded, not of the data type into which you want to scan its contents.

Answer 2

Your problem is the wscanf format.

As described on MAN :

s

Matches a sequence of non white-space wide characters. [...] The application shall ensure that the corresponding argument is a pointer to a character array large enough to accept the sequence and the terminating null character, which shall be added automatically.

Simply "%s" must be used for non-wide-chars string, as usual in printf , scanf and so on

MAN also says:

l (ell)

Specifies that a following d, i, o, u, x, X, or n conversion specifier applies to an argument with type pointer to long or unsigned long; [...] that a following c, s, or [ conversion specifier applies to an argument with type pointer to wchar_t.

That means you must use "%ls" as format string to read a wide-char string.

There is another non-standard ISO C solution if you are on POSIX or on .NET MSDN : format "%S" can be used.