Insert integer into the middle of string c-CodePudding

I am trying to replace the W with the number 5 (in this example). However, when I try, I only get the the ascii value of 5 to replace the W, instead of the number 5 itself. How would I fix this?
NOTE: I this is a shortened example from a longer project. I need to access the number in nums[1].

#include <iostream>
#include <string>

using namespace std;

int main()
{
    int nums[3] {4,5,6};
    string str = "HELLO WORLD";

    cout << str << endl;
    str[6] = nums[1];
    cout << str << endl;

    return 0;
}

Output:
HELLO WORLD
HELLO ♣ORLD

CodePudding user response：

You are trying to store an int where a char is expected. Integer 5 (interpreted as character '♣' in your console's charset) and character '5' (integer 53 in ASCII) are not the same value.

Try this instead:

#include <iostream>
#include <string>

using namespace std;

int main()
{
    char ch0 = '5';
    string str = "HELLO WORLD";

    cout << str << endl;
    str[6] = ch0;
    cout << str << endl;

    return 0;
}

CodePudding user response：

You can convert a digit to an ASCII character: char c = '0' 5 (gives you '5').
This is your code fixed:

#include <iostream>
#include <string>

using namespace std;

int main()
{
    int nums[3] {4,5,6};
    string str = "HELLO WORLD";

    cout << str << endl;
    str[6] = '0'   nums[1];
    cout << str << endl;

    return 0;
}

However, if you intend to insert an integer as you title says, you have to do this:

#include <iostream>
#include <string>

using namespace std;

int main()
{
    int nums[3] {4,15,6};
    string str = "HELLO WORLD";

    cout << str << endl;
    str = str.substr(0, 6)   std::to_string(nums[1])   str.substr(7);
    cout << str << endl;

    return 0;
}

Here is a more sophisticated version which tries to use existing capacity:


#include <iostream>
#include <string>
#include <algorithm>

// don't ever do it with std
// using namespace std;

size_t count_digits(int num)
{
    int digits = 0; 
    do { 
        num /= 10; 
        digits  ; 
    } while (num);
    return digits;
}

void insert_number(std::string& str, size_t indx, int num)
{
    const size_t digits = count_digits(num),
        oldSize = str.size();
    
    // insert will reallocate only if capacity is not enough
    str.insert(str.size(), digits - 1, '0');

    // move the end of string right by rotating (rewriting characters)
    auto iterBegin = std::next(str.begin(), indx),
        iterNext = std::next(str.begin(), oldSize);
    std::rotate(iterBegin, iterNext, str.end());

    // write our string from integer to the designated space
    const auto &strInteger = std::to_string(num);
    for (size_t iStr = indx, iInt = 0; iInt != strInteger.size();   iInt,   iStr)
        str[iStr] = strInteger[iInt];
}

int main()
{
    int nums[3] {4, 48152342, 6};
    std::string str = "HELLO WORLD LOOOOONG STRIIING";
    str.reserve(str.capacity()   20); // strings don't preallocate more space after construction

    std::cout << str << std::endl;
    std::cout << "capacity before: " << str.capacity() << std::endl;
    insert_number(str, 6, nums[1]);
    std::cout << str << std::endl;
    std::cout << "capacity after: " << str.capacity() << std::endl;

    return 0;
}

https://godbolt.org/z/7aPMvcosj