从包含其他字符的字符串中提取尾随 int

Question

关于从 C++ 中的字符串中提取有符号整数，我遇到了问题。假设我有一个字符串 images1234，我如何在不知道 C++ 中最后一个非数字字符的位置的情况下从字符串中提取 1234。

仅供参考，我已经尝试过 stringstream 以及其他人通过 post 建议的 lexical_cast 但是 stringstream returns 0 而 lexical_cast 停止工作。

int main()
{
    string virtuallive("Images1234");
    //stringstream output(virtuallive.c_str());
    //int i = stoi(virtuallive);
    //stringstream output(virtuallive);
    int i;
    i = boost::lexical_cast<int>(virtuallive.c_str());
    //output >> i;
    cout << i << endl;
    return 0;
}

Answer 1

How can i extract the 1234 from the string without knowing the position of the last non numeric character in C++?

你不能。不过位置不难找：

auto last_non_numeric = input.find_last_not_of("1234567890");
char* endp = &input[0];
if (last_non_numeric != std::string::npos)
    endp += last_non_numeric + 1;
if (*endp) { /* FAILURE, no number on the end */ }
auto i = strtol(endp, &endp, 10);
if (*endp) {/* weird FAILURE, maybe the number was really HUGE and couldn't convert */}

Answer 2

另一种可能性是将字符串放入 stringstream，然后从流中读取数字（在为流注入一个将除数字以外的所有内容都分类为白色 space 的语言环境之后）。

// First the desired facet:
struct digits_only: std::ctype<char> {
    digits_only(): std::ctype<char>(get_table()) {}

    static std::ctype_base::mask const* get_table() {
        // everything is white-space:
        static std::vector<std::ctype_base::mask> 
            rc(std::ctype<char>::table_size,std::ctype_base::space);

        // except digits, which are digits
        std::fill(&rc['0'], &rc['9'], std::ctype_base::digit);

        // and '.', which we'll call punctuation:
        rc['.'] = std::ctype_base::punct;
        return &rc[0];
    }
};

然后是读取数据的代码：

std::istringstream virtuallive("Images1234");
virtuallive.imbue(locale(locale(), new digits_only);

int number;

// Since we classify the letters as white space, the stream will ignore them.
// We can just read the number as if nothing else were there:
virtuallive >> number;

当流包含大量数据并且您希望所有流中的数据以相同方式解释时（例如，仅阅读数字，不管它可能包含什么）。

从包含其他字符的字符串中提取尾随 int

Extract trailing int from string containing other characters

c++11

visual-c++

string-parsing