Looping until string length is divisible by 16. (C )-CodePudding

So I was coding a program that takes the length of a given string, then loop through it until it is divisible by 16. I don't know what's going on in the program but it spits this error out:

terminate called after throwing an instance of std::length_error' what(): basic_string::_M_replace_aux

I expect an output of the text padded with 0's and the length being divisible by 16

Heres the code


#include <iostream>
#include <string.h>

using namespace std;

int check(string usrinp) {
    if (usrinp.length() % 16 != 0) {
        for (int i = 0; i < usrinp.length(); i  ) {
            if (usrinp.length() % 2 != 0) {
                usrinp.append(15 - usrinp.length(), '0');
            }
            else {
                usrinp.append(16 - usrinp.length(), '0');
            }
        }
    }

    cout << usrinp;
    return 0;
}

int main(){
    check("1");
}

CodePudding user response：

It is not very clear what question is asking about. So I implemented two interpretations of your question.

First variant, when you have to make a multiple of 16 by repeating a string, then you just have to use LCM (Least Common Multiple), your target string size is equal target_size = LCM(original_string.size(), 16).

Second solution is when you have to pad a string to multiple of 16. Then your resulting size is equal to target_size = (original_string.size() 15) / 16 * 16.

Try it online!

#include <numeric>
#include <iostream>
#include <string>

std::string RepeatToMultiple(std::string const & s, size_t k) {
    size_t const cnt = std::lcm(s.size(), k) / s.size();
    auto r = s;
    for (size_t i = 1; i < cnt;   i)
        r  = s;
    return r;
}

std::string PadToMultiple(std::string s, size_t k, char fill = '0') {
    s.resize((s.size()   k - 1) / k * k, fill);
    return s;
}

int main() {
    std::string s = "abcde_";
    std::cout << "Original: (size " << s.size() << ") " << s << std::endl;
    auto r = RepeatToMultiple(s, 16);
    std::cout << "Repeated till multiple of 16: (size " << r.size() << ") " << r << std::endl;
    auto r2 = PadToMultiple(s, 16);
    std::cout << "Padded to multiple of 16: (size " << r2.size() << ") " << r2 << std::endl;
}

Output:

Original: (size 6) abcde_
Repeated till multiple of 16: (size 48) abcde_abcde_abcde_abcde_abcde_abcde_abcde_abcde_
Padded to multiple of 16: (size 16) abcde_0000000000

CodePudding user response：

What you want is to calculate your padding correctly:

int pad = 16 * (str.length() / 16   1) - str.length();

Example1:

length of string = 4
then required pad = 12

16 * (4 / 16 1) - 4 gives 12. Don't be mistaken by (4 / 16), it'll result in 0 for integer division.

Example2:

length of string = 37 then required pad = 11

16 * (37 / 16 1) - 37 gives 11.

Then you can use whatever function you require to append to the string.

str.append(pad, '0');