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According to this reference, I should be able to match a single digit with
std::regex e1 ("\\d");
However, when I run the following test code I get a regex exception.
#include <iostream>
#include <string>
#include <regex>
int main()
{
std::regex r("\\d");
std::string s("9");
if (std::regex_match(s, r)) { std::cout << "matched!" << std::endl; }
}
933
The regex [0-9] matches single-digit numbers 0 to 9. [1-9][0-9] matches double-digit numbers 10 to 99. That's the easy part. Matching the three-digit numbers is a little more complicated, since we need to exclude numbers 256 through 999.
1.2 Example: Numbers [0-9]+ or \d+ It matches any SINGLE character in the list. In this example, [0-9] matches any SINGLE character between 0 and 9 (i.e., a digit), where dash ( - ) denotes the range.
The C++ standard library supports multiple regular expression grammars.
Match(String) Searches the specified input string for the first occurrence of the regular expression specified in the Regex constructor. Match(String, Int32) Searches the input string for the first occurrence of a regular expression, beginning at the specified starting position in the string.
GCC's std::regex support is not yet ready for prime time. See: Is gcc 4.8 or earlier buggy about regular expressions?
149
If std::regex support is still buggy as @qwrrty suggests, the character class '[0-9]' is a substitute for '\d'.
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