How to use UTF-8 in C code?

Question

My setup: gcc-4.9.2, UTF-8 environment.

The following C-program works in ASCII, but does not in UTF-8.

Create input file:

echo -n \'привет мир\'          


        

Answer 1

Siddhartha Ghosh's answer gives you the basic problem. Fixing your code requires more work, though.

I used the following script (chk-utf8-test.sh):

echo -n 'привет мир' > вход
make utf8-test
./utf8-test
grep -q 'привет мир' выход && echo OK

I called your program utf8-test.c and amended the source like this, removing the references to /tmp, and being more careful with lengths:

#include 
#include 
#include 

#define SIZE 40

int main(void)
{
    char buf[SIZE + 1];
    char *pat = "привет мир";
    char str[SIZE + 2];

    FILE *f1 = fopen("вход", "r");
    FILE *f2 = fopen("выход", "w");

    if (f1 == 0 || f2 == 0)
    {
        fprintf(stderr, "Failed to open one or both files\n");
        return(1);
    }

    size_t nbytes;
    if ((nbytes = fread(buf, 1, SIZE, f1)) > 0)
    {
        buf[nbytes] = 0;

        if (strncmp(buf, pat, nbytes) == 0)
        {
            sprintf(str, "%.*s\n", (int)nbytes, buf);
            fwrite(str, 1, nbytes, f2);
        }
    }

    fclose(f1);
    fclose(f2);

    return(0);
}

And when I ran the script, I got:

$ bash -x chk-utf8-test.sh
+ '[' -f /etc/bashrc ']'
+ . /etc/bashrc
++ '[' -z '' ']'
++ return
+ alias 'r=fc -e -'
+ echo -n 'привет мир'
+ make utf8-test
gcc -O3 -g -std=c11 -Wall -Wextra -Werror utf8-test.c -o utf8-test
+ ./utf8-test
+ grep -q 'привет мир' $'в?\213?\205од'
+ echo OK
OK
$

For the record, I was using GCC 5.1.0 on Mac OS X 10.10.3.