提取功能
string extractStr(string str, string regExpStr) {
regex regexp(regExpStr);
smatch m;
regex_search(str, m, regexp);
string result = "";
for (string x : m)
result = result x;
return result;
}
主要代碼
#include <iostream>
#include <regex>
using namespace std;
string extractStr(string, string);
int main(void) {
string test = "(1 1)*(n n)";
cout << extractStr(test, "n\\ n") << endl;
cout << extractStr(test, "(\\d)\\ \\1") << endl;
cout << extractStr(test, "([a-zA-Z])[ -/*]\\1") << endl;
cout << extractStr(test, "([a-zA-Z])[ -/*]([a-zA-Z])") << endl;
return 0;
}
輸出
String = (1 1)*(n n)
n\ n = n n
(\d)\ \1 = 1 11
([a-zA-Z])[ -/*]\1 = n nn
([a-zA-Z])[ -/*]([a-zA-Z]) = n nnn
如果有人可以指出我所做的錯誤或指出我在搜索時遺漏的類似問題，將不勝感激。
uj5u.com熱心網友回復：
C 中的正則運算式不像“普通”正則運算式那樣作業。特別是當您稍后尋找多個組時。我在這里也有一些 C 技巧（常量和參考）。
#include <cassert>
#include <iostream>
#include <sstream>
#include <regex>
#include <string>
// using namespace std; don't do this!
// https://stackoverflow.com/questions/1452721/why-is-using-namespace-std-considered-bad-practice
// pass strings by const reference
// 1. const, you promise not to change them in this function
// 2. by reference, you avoid making copies
std::string extractStr(const std::string& str, const std::string& regExpStr)
{
std::regex regexp(regExpStr);
std::smatch m;
std::ostringstream os; // streams are more efficient for building up strings
auto begin = str.cbegin();
bool comma = false;
// C matches regexes in parts so work you need to loop
while (std::regex_search(begin, str.end(), m, regexp))
{
if (comma) os << ", ";
os << m[0];
comma = true;
begin = m.suffix().first;
}
return os.str();
}
// small helper function to produce nicer output for your tests.
void test(const std::string& input, const std::string& regex, const std::string& expected)
{
auto output = extractStr(input, regex);
if (output == expected)
{
std::cout << "test succeeded : output = " << output << "\n";
}
else
{
std::cout << "test failed : output = " << output << ", expected : " << expected << "\n";
}
}
int main(void)
{
std::string input = "(1 1)*(n n)";
test(input, "n\\ n", "n n");
test(input, "(\\d)\\ \\1", "1 1");
test(input, "([a-zA-Z])[ -/*]\\1", "n n");
return 0;
}
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