c - How to read unicode (utf-8) / binary file line by line

Question

Hi programmers,

I want read line by line a Unicode (UTF-8) text file created by Notepad, i don't want display the Unicode string in the screen, i want just read and compare the strings!.

This code read ANSI file line by line, and compare the strings

What i want

Read test_ansi.txt line by line

if the line = "b" print "YES!"

else print "NO!"

read_ansi_line_by_line.c

#include <stdio.h>

int main()
{
    char *inname = "test_ansi.txt";
    FILE *infile;
    char line_buffer[BUFSIZ]; /* BUFSIZ is defined if you include stdio.h */
    char line_number;

    infile = fopen(inname, "r");
    if (!infile) {
        printf("
file '%s' not found
", inname);
        return 0;
    }
    printf("
%s

", inname);

    line_number = 0;
    while (fgets(line_buffer, sizeof(line_buffer), infile)) {
        ++line_number;
        /* note that the newline is in the buffer */
        if (strcmp("b
", line_buffer) == 0 ){
            printf("%d: YES!
", line_number);
        }else{
            printf("%d: NO!
", line_number,line_buffer);
        }
    }
    printf("

Total: %d
", line_number);
    return 0;
}

test_ansi.txt

a
b
c

Compiling

gcc -o read_ansi_line_by_line read_ansi_line_by_line.c

Output

test_ansi.txt

1: NO!
2: YES!
3: NO!


Total: 3

Now i need read Unicode (UTF-8) file created by Notepad, after more than 6 months i don't found any good code/library in C can read file coded in UTF-8!, i don't know exactly why but i think the standard C don't support Unicode!

Reading Unicode binary file its OK!, but the probleme is the binary file most be already created in binary mode!, that mean if we want read a Unicode (UTF-8) file created by Notepad we need to translate it from UTF-8 file to BINARY file!

This code write Unicode string to a binary file, NOTE the C file is coded in UTF-8 and compiled by GCC

What i want

Write the Unicode char "?" to test_bin.dat

create_bin.c

#define UNICODE
#ifdef UNICODE
#define _UNICODE
#else
#define _MBCS
#endif

#include <stdio.h>
#include <wchar.h>

int main()
{
     /*Data to be stored in file*/
     wchar_t line_buffer[BUFSIZ]=L"?";
     /*Opening file for writing in binary mode*/
     FILE *infile=fopen("test_bin.dat","wb");
     /*Writing data to file*/
     fwrite(line_buffer, 1, 13, infile);
     /*Closing File*/
     fclose(infile);

    return 0;
}

Compiling

gcc -o create_bin create_bin.c

Output

create test_bin.dat

Now i want read the binary file line by line and compare!

What i want

Read test_bin.dat line by line if the line = "?" print "YES!" else print "NO!"

read_bin_line_by_line.c

#define UNICODE
#ifdef UNICODE
#define _UNICODE
#else
#define _MBCS
#endif

#include <stdio.h>
#include <wchar.h>

int main()
{
    wchar_t *inname = L"test_bin.dat";
    FILE *infile;
    wchar_t line_buffer[BUFSIZ]; /* BUFSIZ is defined if you include stdio.h */

    infile = _wfopen(inname,L"rb");
    if (!infile) {
        wprintf(L"
file '%s' not found
", inname);
        return 0;
    }
    wprintf(L"
%s

", inname);

    /*Reading data from file into temporary buffer*/
    while (fread(line_buffer,1,13,infile)) {
        /* note that the newline is in the buffer */
        if ( wcscmp ( L"?" , line_buffer ) == 0 ){
             wprintf(L"YES!
");
        }else{
             wprintf(L"NO!
", line_buffer);
        }
    }
    /*Closing File*/
    fclose(infile);
    return 0;
}

Output

test_bin.dat

YES!

---

THE PROBLEM

This method is VERY LONG! and NOT POWERFUL (i m beginner in software engineering)

Please any one know how to read Unicode file ? (i know its not easy!) Please any one know how to convert Unicode file to Binary file ? (simple method) Please any one know how to read Unicode file in binary mode ? (i m not sure)

Thank You.

Answer 1

A nice property of UTF-8 is that you do not need to decode in order to compare it. The order returned from strcmp will be the same whether you decode it first or not. So just read it as raw bytes and run strcmp.