我原以为这很简单,但它出现了一些困难。如果我有

std::string name = "John";
int age = 21;

我如何结合他们得到一个单一的字符串“John21”?


当前回答

你可以像这样使用C函数itoa():

    char buf[3];
    itoa(age, buf, 10);
    name += buf;

其他回答

我写了一个函数,它以int数作为参数,并将其转换为字符串字面量。此函数依赖于另一个函数,该函数将单个数字转换为其char等价:

char intToChar(int num)
{
    if (num < 10 && num >= 0)
    {
        return num + 48;
        //48 is the number that we add to an integer number to have its character equivalent (see the unsigned ASCII table)
    }
    else
    {
        return '*';
    }
}

string intToString(int num)
{
    int digits = 0, process, single;
    string numString;
    process = num;

    // The following process the number of digits in num
    while (process != 0)
    {
        single  = process % 10; // 'single' now holds the rightmost portion of the int
        process = (process - single)/10;
        // Take out the rightmost number of the int (it's a zero in this portion of the int), then divide it by 10
        // The above combination eliminates the rightmost portion of the int
        digits ++;
    }

    process = num;

    // Fill the numString with '*' times digits
    for (int i = 0; i < digits; i++)
    {
        numString += '*';
    }


    for (int i = digits-1; i >= 0; i--)
    {
        single = process % 10;
        numString[i] = intToChar ( single);
        process = (process - single) / 10;
    }

    return numString;
}

在c++ 11中,你可以使用std::to_string,例如:

auto result = name + std::to_string( age );

std:: ostringstream

<sstream>#include std::ostringstream s; 与<<“约翰”<<年龄; std::string query(s.str());

std:: to_string (C + + 11)

std::string查询("John " + std::to_string(年龄));

boost:: lexical_cast

# include <刺激/ lexical_cast.hpp > std::string查询("John " + boost::lexical_cast<std::string>(age));

有更多的选项可以用来连接整数(或其他数字对象)与字符串。它就是Boost。格式

#include <boost/format.hpp>
#include <string>
int main()
{
    using boost::format;

    int age = 22;
    std::string str_age = str(format("age is %1%") % age);
}

还有Boost的Karma。精神(v2)

#include <boost/spirit/include/karma.hpp>
#include <iterator>
#include <string>
int main()
{
    using namespace boost::spirit;

    int age = 22;
    std::string str_age("age is ");
    std::back_insert_iterator<std::string> sink(str_age);
    karma::generate(sink, int_, age);

    return 0;
}

提振。Spirit Karma声称是整数到字符串转换的最快选择之一。

下面是如何使用IOStreams库中的解析和格式化aspect将int附加到字符串的实现。

#include <iostream>
#include <locale>
#include <string>

template <class Facet>
struct erasable_facet : Facet
{
    erasable_facet() : Facet(1) { }
    ~erasable_facet() { }
};

void append_int(std::string& s, int n)
{
    erasable_facet<std::num_put<char,
                                std::back_insert_iterator<std::string>>> facet;
    std::ios str(nullptr);

    facet.put(std::back_inserter(s), str,
                                     str.fill(), static_cast<unsigned long>(n));
}

int main()
{
    std::string str = "ID: ";
    int id = 123;

    append_int(str, id);

    std::cout << str; // ID: 123
}