The width specifier in printf does not work properly with accented characters

Question

I'm trying to format output of some strings in c with the width specifier and the printf-function. However I'm having trouble getting the behaviour I want. It seems that everytime printf encounters the character å, ä or ö the the width reserved for the string gets one position smaller.

A code-snippet to illustrate:

#include <stdio.h>

int main(void)
{
  printf(">%-10s<\n", "aoa");
  printf(">%-10s<\n", "aäoa");
  printf(">%-10s<\n", "aäoöa");
  printf(">%-10s<\n", "aäoöaå");

  return 0;
}

Outputs in my ubuntu linux bash-shell.

>aoa       <
>aäoa     <
>aäoöa   <
>aäoöaå <

I'm looking for advice on how to deal with this. What I want is for all the strings in the snippet above to print within space-padded 10 char wide field like so:

>aoa       <
>aäoa      <
>aäoöa     <
>aäoöaå    <

I also appreciate any insight as to why this is happening or feedback if this is not an issue with other setups.

Answer 1

Use wide character strings and wprintf:

#include <cwchar>
#include <locale.h>

int main(void)
{
  // seems to be needed for the correct output encoding
  setlocale(LC_ALL, "");

  wprintf(L">%-10ls<\n", L"aoa");
  wprintf(L">%-10ls<\n", L"aäoa");
  wprintf(L">%-10ls<\n", L"aäoöa");
  wprintf(L">%-10ls<\n", L"aäoöaå");

  return 0;
}

Answer 2

why this is happening?

Take a look to The Absolute Minimum Every Software Developer Absolutely, Positively Must Know About Unicode and Character Sets

As an alternative to wide chars and under UTF8, you can use this function to count the number of non-ASCII chars, then, you can add the result to the width specifier of printf:

#include <stdio.h>

int func(const char *str)
{
    int len = 0;

    while (*str != '\0') {
        if ((*str & 0xc0) == 0x80) {
            len++;
        }
        str++;
    }
    return len;
}

int main(void)
{
    printf(">%-*s<\n", 10 + func("aoa"), "aoa");
    printf(">%-*s<\n", 10 + func("aäoa"), "aäoa");
    printf(">%-*s<\n", 10 + func("aäoöa"), "aäoöa");
    printf(">%-*s<\n", 10 + func("aäoöaå"), "aäoöaå");
    return 0;
}

Output:

>aoa       <
>aäoa      <
>aäoöa     <
>aäoöaå    <