So, here is some simple code to recreate my issue:
#include <cstdio>
const char* badString = u8"aš𒀀";
const char* anotherBadString = u8"\xef\x96\xae\xef\x96\xb6\x61\xc5\xa1\xf0\x92\x80\x80";
const char* goodString = "\xef\x96\xae\xef\x96\xb6\x61\xc5\xa1\xf0\x92\x80\x80";
void printHex(const char* str)
{
for (; *str; ++str)
{
printf("%02X ", *str & 0xFF);
}
puts("");
}
int main(int argc, char *argv[])
{
printHex(badString);
printHex(anotherBadString);
printHex(goodString);
return 0;
}
I would expect all of these strings to print out the same result, EF 96 AE EF 96 B6 61 C5 A1 F0 92 80 80 . However, in MSVC 2019, the first two strings print out C3 AF C2 96 C2 AE C3 AF C2 96 C2 B6 61 C3 85 C2 A1 C3 B0 C2 92 C2 80 C2 80. This seems to be a result of encoding into UTF-8 an extra time.
I've read in other threads that a solution to this problem is to add the /utf-8 flag to the project, but I've tried that and it doesn't make any difference. Is there something more fundamental that I'm not understanding here?
Thanks a bunch!
The first character of the first string is ï (U+00EF, Latin Small Letter I With Diaeresis), whose UTF-8 encoding is C3 AF.
You apparently want the first string to begin with U+F5AE, but whatever editor you opened the source file in agrees with MSVC that it doesn't begin with that character.
The source file is probably encoded as UTF-8 with a BOM, and that's why the /utf-8 flag doesn't change anything. The string was corrupted at some point, and now its corrupted form is faithfully represented in the file, and MSVC is faithfully preserving it in the compiled code.
The second string begins with \xef, which MSVC is interpreting as equivalent to \u00ef, which is ï again. I can't find any clear statement in the C++20 draft standard regarding what \x is supposed to mean in UTF-8 strings (although I didn't look very hard). From experimentation, it appears that most compilers other than MSVC treat \x followed by hex digits as a literal byte, even if that makes the string not valid UTF-8. I think you shouldn't use \x in u8 prefixed strings because it isn't portable (except for \x00 through \x7f, probably). If you want U+F5AE then write \uf5ae.
Related
Diacritic Wikipedia
I've build an EEPROM (Kind of like a very low tech USB stick) Programmer and I'm writing a program witch reads text from a txt file and then converts it into bin/hex that the programmer can use to program the data onto the EEPROM. I've got everything except for a function that converts the string into hex. I've tried using this code which works somewhat well.
string Text = "This is a string.";
for(int i = 0; i < Text.size(); i++) {
cout << uppercase << hex << (int)Text[i] << " ";
}
This will out put this:
54 68 69 73 20 69 73 20 61 20 73 74 72 69 6E 67 2E
But when giving it:
Thïs ìs â stríng.
It wil retun this:
54 68 FFFFFFC3 FFFFFFAF 73 20 FFFFFFC3 FFFFFFAC 73 20 FFFFFFC3 FFFFFFA2 20 73 74 72 FFFFFFC3 FFFFFFAD 6E 67 2E
This doesn't look right to me. My best guess is that normal char are converted to ASCII and the special ones get converted in some form of Unicode.
Is there a way to make everything Unicode?
Side note The EEPROM can only hold 2k bytes so the more space efficient the better.
So my end goal is:
Make a function that turns a string into its hex equivalent.
With the end result being space efficient and supporting diacritics.
Make another function that could read the hex and turn it into a string, also with support for diacritics.
If that is not possible I'm willing to use a custom formatting that would store an 'ê' like "|e^" for example. With an equivalent of "|" as a way for me to intercept a special character.
Thanks for your help!
a double cast is needed here: first cast the character to (unsigned char), then cast to (int):
(int)(unsigned char)Text[i]
this is necessary because casting as (unsigned int) does not work as you might expect. the signed char value is first widened, then the cast is applied, but at that point, the sign extension has already been performed.
see this on https://godbolt.org/z/GhYz3T8v6
So I am writing a program to turn a Chinese-English definition .txt file into a vocab trainer that runs through the CLI. However, in windows when I try to compile this in VS2017 it turns into gibberish and I'm not sure why. I think it was working OK in linux but windows seems to mess it up quite a bit. Does this have something to do with the encoding table in windows? Am I missing something? I wrote the code in Linux as well as the input file, but I tried writing the characters using windows IME and still has the same result. I think the picture speaks best for itself. Thanks
Note: Added sample of input/output as it appears in Windows, as requested. Also, input is UTF-8.
Sample of input
人(rén),person
刀(dāo),knife
力(lì),power
又(yòu),right hand; again
口(kǒu),mouth
Sample of output
人(rén),person
刀(dāo),knife
力(lì),power
又(yòu),right hand; again
口(kǒu),mouth
土(tǔ),earth
Picture of Input file & Output
TL;DR: The Windows terminal hates Unicode. You can work around it, but it's not pretty.
Your issues here are unrelated to "char versus wchar_t". In fact, there's nothing wrong with your program! The problems only arise when the text leaves through cout and arrives at the terminal.
You're probably used to thinking of a char as a "character"; this is a common (but understandable) misconception. In C/C++, the char type is usually synonymous with an 8-bit integer, and thus is more accurately described as a byte.
Your text file chineseVocab.txt is encoded as UTF-8. When you read this file via fstream, what you get is a string of UTF-8-encoded bytes.
There is no such thing as a "character" in I/O; you're always transmitting bytes in a particular encoding. In your example, you are reading UTF-8-encoded bytes from a file handle (fin).
Try running this, and you should see identical results on both platforms (Windows and Linux):
int main()
{
fstream fin("chineseVocab.txt");
string line;
while (getline(fin, line))
{
cout << "Number of bytes in the line: " << dec << line.length() << endl;
cout << " ";
for (char c : line)
{
// Here we need to trick the compiler into displaying this "char" as an integer:
unsigned int byte = (unsigned char)c;
cout << hex << byte << " ";
}
cout << endl;
cout << endl;
}
return 0;
}
Here's what I see in mine (Windows):
Number of bytes in the line: 16
e4 ba ba 28 72 c3 a9 6e 29 2c 70 65 72 73 6f 6e
Number of bytes in the line: 15
e5 88 80 28 64 c4 81 6f 29 2c 6b 6e 69 66 65
Number of bytes in the line: 14
e5 8a 9b 28 6c c3 ac 29 2c 70 6f 77 65 72
Number of bytes in the line: 27
e5 8f 88 28 79 c3 b2 75 29 2c 72 69 67 68 74 20 68 61 6e 64 3b 20 61 67 61 69 6e
Number of bytes in the line: 15
e5 8f a3 28 6b c7 92 75 29 2c 6d 6f 75 74 68
So far, so good.
The problem starts now: you want to write those same UTF-8-encoded bytes to another file handle (cout).
The cout file handle is connected to your CLI (the "terminal", the "console", the "shell", whatever you wanna call it). The CLI reads bytes from cout and decodes them into characters so they can be displayed.
Linux terminals are usually configured to use a UTF-8 decoder. Good news! Your bytes are UTF-8-encoded, so your Linux terminal's decoder matches the text file's encoding. That's why everything looks good in the terminal.
Windows terminals, on the other hand, are usually configured to use a system-dependent decoder (yours appears to be DOS codepage 437). Bad news! Your bytes are UTF-8-encoded, so your Windows terminal's decoder does not match the text file's encoding. That's why everything looks garbled in the terminal.
OK, so how do you solve this? Unfortunately, I couldn't find any portable way to do it... You will need to fork your program into a Linux version and a Windows version. In the Windows version:
Convert your UTF-8 bytes into UTF-16 code units.
Set standard output to UTF-16 mode.
Write to wcout instead of cout
Tell your users to change their terminals to a font that supports Chinese characters.
Here's the code:
#include <fstream>
#include <iostream>
#include <string>
#include <windows.h>
#include <fcntl.h>
#include <io.h>
#include <stdio.h>
using namespace std;
// Based on this article:
// https://msdn.microsoft.com/magazine/mt763237?f=255&MSPPError=-2147217396
wstring utf16FromUtf8(const string & utf8)
{
std::wstring utf16;
// Empty input --> empty output
if (utf8.length() == 0)
return utf16;
// Reject the string if its bytes do not constitute valid UTF-8
constexpr DWORD kFlags = MB_ERR_INVALID_CHARS;
// Compute how many 16-bit code units are needed to store this string:
const int nCodeUnits = ::MultiByteToWideChar(
CP_UTF8, // Source string is in UTF-8
kFlags, // Conversion flags
utf8.data(), // Source UTF-8 string pointer
utf8.length(), // Length of the source UTF-8 string, in bytes
nullptr, // Unused - no conversion done in this step
0 // Request size of destination buffer, in wchar_ts
);
// Invalid UTF-8 detected? Return empty string:
if (!nCodeUnits)
return utf16;
// Allocate space for the UTF-16 code units:
utf16.resize(nCodeUnits);
// Convert from UTF-8 to UTF-16
int result = ::MultiByteToWideChar(
CP_UTF8, // Source string is in UTF-8
kFlags, // Conversion flags
utf8.data(), // Source UTF-8 string pointer
utf8.length(), // Length of source UTF-8 string, in bytes
&utf16[0], // Pointer to destination buffer
nCodeUnits // Size of destination buffer, in code units
);
return utf16;
}
int main()
{
// Based on this article:
// https://blogs.msmvps.com/gdicanio/2017/08/22/printing-utf-8-text-to-the-windows-console/
_setmode(_fileno(stdout), _O_U16TEXT);
fstream fin("chineseVocab.txt");
string line;
while (getline(fin, line))
wcout << utf16FromUtf8(line) << endl;
return 0;
}
In my terminal, it mostly looks OK after I change the font to MS Gothic:
Some characters are still messed up, but that's due to the font not supporting them.
#include <iostream>
#include <fstream>
using namespace std;
struct example
{
int num1;
char abc[10];
}obj;
int main ()
{
ofstream myfile1 , myfile2;
myfile1.open ("example1.txt");
myfile2.open ("example2.txt");
myfile1 << obj.num1<<obj.abc; //instruction 1
myfile2.write((char*)&obj, sizeof(obj)); //instruction 2
myfile1.close();
myfile2.close();
return 0;
}
In this example will both the example files be identical with data or different? Are instruction 1 and instruction 2 same?
There's a massive difference.
Approach 1) writes the number using ASCII encoding, so there's an ASCII-encoded byte for each digit in the number. For example, the number 28 is encoded as one byte containing ASCII '2' (value 50 decimal, 32 hex) and another for '8' (56 / 0x38). If you look at the file in a program like less you'll be able to see the 2 and the 8 in there as human-readable text. Then << obj.abc writes the characters in abc up until (but excluding) the first NUL (0-value byte): if there's no NUL you run off the end of the buffer and have undefined behaviour: your program may or may not crash, it may print nothing or garbage, all bets are off. If your file is in text mode, it might translate any newline and/or carriage return characters in abc1 to some other standard representation of line breaks your operating system uses (e.g. it might automatically place a carriage return after every newline you write, or remove carriage returns that were in abc1).
Approach 2) writes the sizeof(obj) bytes in memory: that's a constant number of bytes regardless of their content. The number will be stored in binary, so a program like less won't show you the human-readable number from num1.
Depending on the way your CPU stores numbers in memory, you might have the bytes in the number stored in different orders in the file (something called endianness). There'll then always be 10 characters from abc1 even if there's a NUL in there somewhere. Writing out binary blocks like this is normally substantially faster than converting number to ASCII text and the computer having to worry about if/where there are NULs. Not that you normally have to care, but not all the bytes written necessarily contribute to the logical value of obj: some may be padding.
A more subtle difference is that for approach 1) there are ostensibly multiple object states that could produce the same output. Consider {123, "45"} and {12345, ""} -> either way you'd print "12345". So, you couldn't later open and read from the file and be sure to set num1 and abc to what they used to be. I say "ostensibly" above because you might happen to have some knowledge we don't, such as that the abc1 field will always start with a letter. Another problem is knowing where abc1 finishes, as its length can vary. If these issues are relevant to your actual use (e.g. abc1 could start with a digit), you could for example write << obj.num1 << ' ' << obj.abc1 << '\n' so the space and newline would tell you where the fields end (assuming abc1 won't contain newlines: if it could, consider another delimiter character or an escaping/quoting convention). With the space/newline delimiters, you can read the file back by changing the type of abc1 to std::string to protect against overruns by corrupt or tampered-with files, then using if (inputStream >> obj.num1 && getline(inputStream, obj.abc1)) ...process obj.... getline can cope with embedded spaces and will read until a newline.
Example: {258, "hello\0\0\0\0\0"} on a little-endian system where sizeof(int) is 32 and the stucture's padded out to 12 bytes would print (offsets and byte values shown in hexadecimal):
bytes in file at offset...
00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f
approach 1) 32 35 38 69 65 6c 6c 6f
'2' '5' '8' 'h' 'e' 'l' 'l' 'o'
approach 2) 00 00 01 02 69 65 6c 6c 6f 00 00 00 00 00 00 00
[-32 bit 258-] 'h' 'e' 'l' 'l' 'o''\0''\0''\0''\0''\0' pad pad
Notes: for approach 2, 00 00 01 02 encodes 100000010 binary which is 258 decimal. (Search for "binary encoding" to learn more about this).
I encountered an odd problem when exporting float values to a file. I would expect every float to be of the same length (obviously), but my programme sometimes exports it a 32 bit number and sometimes as a 40 bit number.
A minimal working example of a programme that still shows this behaviour is:
#include <stdio.h>
const char* fileName = "C:/Users/Path/To/TestFile.txt";
float array [5];
int main(int argc, char* argv [])
{
float temp1 = 1.63006e-33f;
float temp2 = 1.55949e-32f;
array[0] = temp1;
array[1] = temp2;
array[2] = temp1;
array[3] = temp2;
array[4] = temp2;
FILE* outputFile;
if (!fopen_s(&outputFile, fileName, "w"))
{
fwrite(array, 5 * sizeof(float), 1, outputFile);
fclose(outputFile);
}
return true;
}
I would expect the output file to contain exactly 20 (5 times 4) bytes, each four of which represent a float. However, I get this:
8b 6b 07 09 // this is indeed 1.63006e-33f
5b f2 a1 0d 0a // I don't know what this is but it's a byte too long
8b 6b 07 09
5b f2 a1 0d 0a
5b f2 a1 0d 0a
So the float temp2 takes 5 bytes instead of four, and the total length of he file is 23. How is this possible?! The number aren't so small that they are subnormal numbers, and I can't think of any other reason why there would be a difference in size.
I am using the MSVC 2010 compiler on a 64-bit Windows 7 system.
Note: I already asked a very similar question here, but when I realised the problem was more general, I decided to repost it in a more concise way.
QDataStream uses sometimes 32 bit and sometimes 40 bit floats
The problem is that on Windows, you have to differentiate between text and binary files. You have the file opened as text, which means 0d (carriage-return) is inserted before every 0a (line-feed) written. Open the file like this:
if (!fopen_s(&outputFile, fileName, "wb"))
The rest as before, and it should work.
You're not writing text; you're writing binary data... However, your file is open for writing text ("w") instead of writing binary ("wb"). Hence, fwrite() is translating '\n' to "\r\n".
Change this:
if (!fopen_s(&outputFile, fileName, "w"))
To this:
if (!fopen_s(&outputFile, fileName, "wb"))
In "wb", the b stands for binary mode.
I'm trying to write a codec for Code page 437. My plan was to just pass the ASCII characters through and map the remaining 128 characters in a table, using the utf-16 value as key.
For some combined charaters (letters with dots, tildes etcetera), the character appears to occupy two QChars.
A test program that prints the utf-16 values for the arguments to the program:
#include <iostream>
#include <QString>
using namespace std;
void print(QString qs)
{
for (QString::iterator it = qs.begin(); it != qs.end(); ++it)
cout << hex << it->unicode() << " ";
cout << "\n";
}
int main(int argc, char *argv[])
{
for (int i = 1; i < argc; i++)
print(QString::fromStdString(argv[i]));
}
Some output:
$ ./utf16 Ç ü é
c3 87
c3 bc
c3 a9
I had expected
c387
c3bc
c3a9
Tried the various normalizationsforms avaialable in QString but no one had fewer bytes than the default.
Since QChar is 2 bytes it should be able to hold the value of the characters above in one object. Why does the QString use two QChars? How can I fetch the combined unicode value?
QString::fromStdString expects an ASCII string and doesn't do any decoding. Use fromLocal8Bit instead.
Your expected output is wrong. For example, Ç is U+00C7, so you should expect C7, not the UTF-8 encoding of C3 87!
If you modify main() as below, you get the expected Unicode code points. For each character, the first line lists the local encoding (here: Utf-8), since fromStdString is essentially a no-op and passes everything straight. The second line lists the correctly decoded Unicode code point index.
$ ./utf16 Ç ü é
c3 87
c7
c3 bc
fc
c3 a9
e9
int main(int argc, char *argv[])
{
for (int i = 1; i < argc; i++) {
print(QString::fromStdString(argv[i]));
print(QString::fromLocal8Bit(argv[i]));
}
}
Just sidestep the problem. See QApplication in Unicode. QApplication::arguments is already UTF-16 encoded for you taking local conventions into account.