i have bit of brain dead moment.
i have store string representation of int char[], ascii representation have left padded spaces. snprintf job.
char data [6]; int msg_len = 10; std::snprintf(data, 6, "%*d", 5, msg_len); //" 10" <-- ok i wonder if there more elegant way it. have access c++11 there's a bit of problem, think snprintf add terminating character, , have avoid that. have intermediary buffer , copy 1 data, add additional complexity.
i need in place, because data structures part of message have send server accepts input formatted way.
the message looks like:
struct { char first_field [6]; char second_field [8]; char data_field [12]; }; and might need set second_field before having set first one. have lot more fields fill in, generic solution appreciated. long can convert int string representation fine.
within indicated constraints may improve on own answer:
#include <algorithm> #include <cstddef> #include <cassert> inline void unsigned_to_decimal( unsigned long number, char* buffer, std::size_t size) { std::size_t = size; buffer[size - 1] = '0'; (unsigned long n ;(n = number) > 0 && > 0 ;) { buffer[--i] = '0' + n - (10 * (number /= 10)); } assert(number == 0); std::fill(buffer,buffer + (i - (i == size)),' '); } for demo, append:
#include <iostream> #include <string> #include <climits> #include <array> constexpr std::size_t decimal_digits(unsigned long n) { return n / 10 > 0 ? 1 + decimal_digits(n / 10) : 1; } int main() { const std::size_t max_digits = decimal_digits(ulong_max); std::cout << "print decimal 0, uint_max, ulong_max " "from left-padded char buffer, size " << max_digits << ":-\n"; (auto ul : std::array<unsigned long,3>{0,uint_max,ulong_max}) { char buf[max_digits]; std::fill(buf,buf + max_digits,'?'); std::cout << '[' << std::string(buf,buf + max_digits) << "]\n"; unsigned_to_decimal(ul,buf,max_digits); std::cout << '[' << std::string(buf,buf + max_digits) << "]\n"; } return 0; } which runs like:
print decimal 0, uint_max, ulong_max left-padded char buffer, size 20:- [????????????????????] [ 0] [????????????????????] [ 4294967295] [????????????????????] [18446744073709551615] (g++ -wall -std=c++11 -pedantic, gcc 5.3.1)
