Question

我是来自Java的C ++新手，所以我需要一些关于我在去的时候遇到的一些基本问题的指导。

我正在读取文件中的行，每行包含6个字符串/整数，它们将作为参数发送到临时变量。

示例：

Local1,Local2,ABC,200,300,asphalt

但是，有两个变量的子类型。一个字符串作为最后一个参数（如上例中的“沥青”）。另一个有一个int而不是。我有一个读取每个参数并将其发送到变量的方法，但是如何检测字符串的最后一位是预先是整数还是字符串，所以我知道是否应该将它发送到Type1变量或Type2变量？

非常感谢！

Answer 1

既然你想确定最后一列的类型，那么这应该有效：

#include <iostream>
#include <string>
#include <cstdlib>
#include <vector>
#include <sstream>
#include <cctype>
#include <algorithm>

enum Types {
    NONE,
    STRING,
    INTEGER,
    DOUBLE
};

struct Found {
    std::string string_val;
    int integer_val;
    double double_val;
    enum Types type;
};

//copied verbatim from:
//http://stackoverflow.com/a/2845275/866930
inline bool isInteger(const std::string &s) {
   if(s.empty() || ((!std::isdigit(s[0])) && (s[0] != '-') && (s[0] != '+'))) return false;

   char * p ;
   std::strtol(s.c_str(), &p, 10);

   return (*p == 0);
}

//modified slightly for decimals:
inline bool isDouble(const std::string &s) {
   if(s.empty() || ((!std::isdigit(s[0])) && (s[0] != '-') && (s[0] != '+'))) return false ;

   char * p ;
   std::strtod(s.c_str(), &p) ;

   return (*p == 0);
}

bool isNotAlpha(char c) {
    return !(std::isalpha(c));
}

//note: this searches for strings containing only characters from the alphabet
//however, you can modify that behavior yourself.
bool isString (const std::string &s) {
    std::string::const_iterator it = std::find_if(s.begin(), s.end(), isNotAlpha);
    return (it == s.end()) ? true : false;
}

void determine_last_column (const std::string& str, Found& found) {
    //reset found:
    found.integer_val = 0;
    found.double_val = 0;
    found.string_val = "";
    found.type = NONE;

    std::string temp;
    std::istringstream iss(str);

    int column = 0;
    char *p;

    while(std::getline(iss, temp, ',')) {
        if (column == 5) {
            //now check to see if the column is an integer or not:
            if (isInteger(temp)) {
                found.integer_val = static_cast<int>(std::strtol(temp.c_str(), &p, 10));
                found.type = INTEGER;
            }
            else if (isDouble(temp)) {
                found.double_val = static_cast<double>(std::strtod(temp.c_str(), &p));
                found.type = DOUBLE;
            }
            else if (isString(temp)) {
                found.string_val = temp;
                found.type = STRING;
            }
        }
        ++column;
    }

    if (found.type == INTEGER) {
        std::cout << "An integer was found: " << found.integer_val << std::endl;
    }
    else if(found.type == DOUBLE) {
        std::cout << "A double was found: " << found.double_val << std::endl;
    }
    else if(found.type == STRING) {
        std::cout << "A string was found: " << found.string_val << std::endl;
    }
    else {
        std::cout << "A valid type was not found! Something went wrong..." << std::endl;
    }
}

int main() {
    std::string line_t1 = "Local1,Local2,ABC,200,300,asphalt";
    std::string line_t2 = "Local1,Local2,ABC,200,300,-7000.3";

    Found found;

    determine_last_column(line_t1, found);
    determine_last_column(line_t2, found);

    return 0;
}

输出并正确分配适当的值：

A string was found: asphalt
An integer was found: -7000.3

此版本适用于int, double, string; 不需要boost ;并且，是普通的C ++ 98。

参考文献：

更新：

此版本现在支持整数或双数的正数和负数，以及字符串。

Answer 2

首先，创建一个可以存储字符串和整数的数组：

std::vector<boost::variant<std::string, int>> items;

其次，在逗号上分割输入字符串：

std::vector<std::string> strings;
boost::split(strings, input, boost::is_any_of(","));

最后，解析每个标记并将其插入到数组中：

for (auto&& string : strings) {
    try {
        items.push_back(boost::lexical_cast<int>(string));
    } catch(boost::bad_lexical_cast const&) {
        items.push_back(std::move(string));
    }
}

C ++检测输入是Int还是String

2 个答案: