In my old C++ project I use to use the gets() command. I've done my research and noticed that it is not reliable anymore and my project won't run with using it.
I use this bit of code right here:
Load(gets(new char[50]));
How would I now get this line of code to work properly? And if you could provide an explanation.
Here's a simple solution:
std::string text;
std::cout << "Enter some text to load: ";
std::getline(cin, text);
Load(text.c_str());
If you must use character arrays, here's a code fragment:
const size_t ARRAY_CAPACITY = 64U;
char text[ARRAY_CAPACITY];
std::cout << "Enter some text to load: ";
cin.getline(&text[0], ARRAY_CAPACITY);
Load(text);
Related
I'm trying to develop function that check whether chinese word which user enters is in the txt file or not. The following is the code. But it is not working. I want to know what the problem is. Help me please.
setlocale(LC_ALL, "Chinese-simplified");
locale::global(locale("Chinese_China"));
SetConsoleOutputCP(936);
SetConsoleCP(936);
bool exist = FALSE;
cout << "\n\n <Find the keyword whether it is in that image or not> \n ";
cout << "Enter word to search for: ";
wstring search;
wcin >> search; //There is a problem to enter chinese.
wfstream file_text("./a.txt");
wstring line;
wstring::size_type pos;
while (getline(file_text, line))
{
pos = line.find(search);
if (pos != wstring::npos) // string::npos is returned if string is not found
{
cout << "Found!" << endl;
exist = true;
break;
}
}
when I use this code, The result is as follows.
const int oldMbcp = _getmbcp();
_setmbcp(936);
const std::locale locale("Chinese_China.936");
_setmbcp(oldMbcp);
If you're interested in more details, please see stod-does-not-work-correctly-with-boostlocale for a more detailed description of how locale works,
In a nutshell the more interesting part for you:
std::stream (stringstream, fstream, cin, cout) has an inner locale-object, which matches the value of the global C++ locale at the moment of the creation of the stream object. As std::in is created long before your code in main is called, it has most probably the classical C locale, no matter what you do afterwards.
you can make sure, that a std::stream object has the desirable locale by invoking std::stream::imbue(std::locale(your_favorit_locale)).
I would like to add the following:
It is almost never a good idea to set the global locale - it might break other parts of the program or third part libraries - you never know.
std::setlocale and locale::global do slightly different things, but locale::global resets not only the global c++-locale but also the c-locale (which is also set by std::setlocale, not to be confused with the classical "C" locale), so you should call it in another order if you want to have c++ locale set to Chinese_China and C locale to chinese-simplified
First
locale::global(locale("Chinese_China"));
And than
setlocale(LC_ALL, "Chinese-simplified");
Try locale::global(locale("Chinese_China.936")); or locale::global(locale(""));
And for LC_ALL "chinese-simplified" or "chs"
If using Vladislav's answer does not solve this, take a look at answer to stl - Shift-JIS decoding fails using wifstrem in Visual C++ 2013 - Stack Overflow:
const int oldMbcp = _getmbcp();
_setmbcp(936);
const std::locale locale("Chinese_China.936");
_setmbcp(oldMbcp);
There appears to be a bug in Visual Studio's implementation of locales. See also c++ - double byte character sequence conversion issue in Visual Studio 2015 - Stack Overflow.
Using fstreams I have a file opened that contains numerous lines. Each contiguos set of 4 lines are such that: the first line is an int, the second and third are strings and fourth is a double. This sequence continues till EOF.
I'm attempting to load these lines into a struct array:
struct Library {
int id;
string title;
string artist;
double price;
};
and the code I'm trying to implement to load data into the struct is this:
const int LIMIT = 10
Library database[LIMIT];
ifstream file;
file.open("list.txt");
if(file) {
while(!(file.eof()) && counter < LIMIT) {
file >> database[counter].id;
getline(file, database[counter].title;
getline(file, database[counter].artist;
file >> database[counter].price;
}
} else {
...
}
// Using the following to debug output
for(int i = 0; i < counter; i++) {
cout << "ID: " << database[i].id << endl
<< "Title: " << database[i].title << endl
<< "Artist: " << database[i].artist << endl
<< "Price: " << database[i].price << endl
<< "-----------------------" << endl;
}
The file I'm trying to throw at this thing is
1234
Never Gonna Give You Up
Rick Astley
4.5
42
Thriller
Michael Jackson
32.1
The problem I'm having here is that between reading the id and title using file >> ... and getline(...) is that somewhere a newline bite is being introduced screwing up the output, which displays this monstrosity...
ID: 1234
Title:
Artist: Never Gonna Give You Up
Price: 0
--------------------
ID: 0
Title:
Artist:
Price: 0
--------------------
The solution is probably the most basic of solutions, but mainly because I can't figure out exactly what is going on with the newline bite I can't combobulate a phrase to shove into google and do my stuff there, and I'm at the stage where I've been looking at a problem so long, basic knowledge isn't working properly - such as how to handle basic input streams.
Any form of help would be much appreciated! Thanks in advance :)
This happens because the >> operator for the input stream only grabs part of a line, and does not always grab the newline character at the end of the line. When followed by a call to getline, the getline will grab the rest of the line previously parsed, not the line after it. There are a few ways to solve this: you can clear the buffer from the input stream after each read, or you can simply get all your input from getline and just parse the resulting strings into an integer or a double when you need to with calls to stoi or stod.
As a side note, you don't want to detect the end of your file the way you presently are. See why is eof considered wrong inside a loop condition?
You can solve this problem by adding:
fflush(file);
everytime before you use getline(file, ...). Basically this will clear the input buffer before you use the getline() function. And fflush() is declared in the cstdio library.
file >> database[counter].id;
will read, in this case, a whitespace separated sequence of characters that is interpreted as an int. The newline is considered whitespace. You should now be sitting on that newline character, thus the getline() will read nothing -- successfully -- and increment the file position just past that.
You may be better off using getline() for each line and then separately interpreting the lines from the reading. For example, the first line read could be interpreted with a subsequent std::stoi() to get the integer representation from the string.
I have been having a very hard time writing to a binary file and reading back. I am basically writing records of this format
1234|ABCD|efgh|IJKL|ABC
Before writing this record, I would write the length of this entire record ( using string.size()) and then I write the record to the binary file using ofstream as follows:
int size;
ofstream studentfile;
studentfile.open( filename.c_str(),ios::out|ios::binary );
studentfile.write((char*)&size,sizeof(int));
studentfile.write(data.c_str(),(data.size()*(sizeof(char))));
cout << "Added " << data << " to " << filename << endl;
studentfile.close();
And I read this data at some other place
ifstream ifile11;
int x;
std::string y;
ifile11.open("student.db", ios::in |ios::binary);
ifile11.read((char*)&x,sizeof(int));
ifile11.read((char*)&y,x);
cout << "X " << x << " Y " << y << endl;
first I read the length of the record into the variable x, and then read the record into string y. The problem is, the output shows x as being '0' and 'y' is empty.
I am not able figure this out. Someone who can look into this problem and provide some insight will be thanked very much.
Thank you
You can't read a string that way, as a std::string is really only a pointer and a size member. (Try doing std::string s; sizeof(s), the size will be constant no matter what you set the string to.)
Instead read it into a temporary buffer, and then convert that buffer into a string:
int length;
ifile11.read(reinterpret_cast<char*>(&length), sizeof(length));
char* temp_buffer = new char[length];
ifile11.read(temp_buffer, length);
std::string str(temp_buffer, length);
delete [] temp_buffer;
I know I am answering my own question, but I strictly feel this information is going to help everyone. For most part, Joachim's answer is correct and works. However, there are two main issues behind my problem :
1. The Dev-C++ compiler was having a hard time reading binary files.
2. Not passing strings properly while writing to the binary file, and also reading from the file. For the reading part, Joachim's answer fixed it all.
The Dev-C++ IDE didn't help me. It wrongly read data from the binary file, and it did it without me even making use of a temp_buffer. Visual C++ 2010 Express has correctly identified this error, and threw run-time exceptions and kept me from being misled.
As soon as I took all my code into a new VC++ project, it appropriately provided me with error messages, so that I could fix it all.
So, please do not use Dev-C++ unless you want to run into real troubles like thiis. Also, when trying to read strings, Joachim's answer would be the ideal way.
I feel pretty stupid, but I'm just starting to learn c++ after coming from other languagues, and I cannot for the life of me comprehend statements that use "<<" and ">>". I know it is simple, but it confuses me every time.
The book I'm using made a really good recommendation to read const declarations from right to left. Is there any similar method for "<<" and ">>"?
i like to say "gets".
cout << "some expression = " << expr << endl;
i'd say that as "cout gets some expression, gets expr, gets endull." similarly if you're reading from a stream, it's your variable that "gets" a value from the input...
On the phone, back when I was a consultant frequently needing to "read aloud" C++ code to clients' employees on the phone, I (explaining once or twice, then they got it) read "input" operator >> as "absorb" and "output" operator << as "emit". "get" and "put" would work just as well if they didn't conflict with alas-too-common other uses. But that doesn't seem to have much to do with right-to-left vs left-to-right, just with your Q's title about "reading aloud" -- "cin absorb x" or "essteedee cout emit blach emit essteedee endl" kinds of "reading code aloud" (e.g. on the phone)!-)
I typically read them from left to right, like so:
cout << setw(6) << val << endl;
"Send to cout, with a width of 6, the contents of val, and then end the line and flush."
or
cin >> val;
"Get from cin the contents of val."
It does take a little bit of special consideration in that you can't just say specific words for each token.
To understand C++, you have to understand that C++ has many of the most powerful tools to build abstractions. cout is nothing but a stream. So, it is very acceptable to mimic the concept of stream.
For example,
std::cout << "hey"; // '<<' is something like the direction of the `data`
throws things in the stream with the same syntax and conventions, infact there is only one syntax for all types.
Also,
std::cin >> number;
extracts the next value of the type specified by number and put it in number.
It just make sense when you think about streams in C++. You can see this in most modern C++ libraries, for example with Boost you can do this:
boost::filesystem::path mypath;
....
mypath = mypath/filename;
The division operator is replaced with '/' or '\' depending on the system you are targeting :)
I never thought too much about it but I suppose you could say "Streams to" or "Streams from" eg.
cout << mysting << endl;
"cout streams from mystring streams from endline"
cin >> myvalue;
"cin streams to myvalue"
I just made that up but it makes sense to me.
This is easy enough the object that the symbol is pointing to on the receiving end. So:
cout << "Enter First Name: ";
cin >> FirstName;
in this code, cout in usually stdout and is "receiving" the characters "Enter First Name", FirstName which is presumably a variable is "receiving" the data from cin which is probably stdin.
A simple way to distinguish the two is like so.
cout << "Some fancy string...";
In this example your are taking a string and sending it to the world (monitor).
cin >> x;
In that one you take an value from the world (keyboard) and save the it into x.
Hence the direction Value >> X.
This looks like homework stuff but please be assured that it isn't homework. Just an exercise in the book we use in our c++ course, I'm trying to read ahead on pointers..
The exercise in the book tells me to split a sentence into tokens and then convert each of them into pig latin then display them..
pig latin here is basically like this: ball becomes allboy in piglatin.. boy becomes oybay.. take the first letter out, put it at the end then add "ay"..
so far this is what i have:
#include <iostream>
using std::cout;
using std::cin;
using std::endl;
#include <cstring>
using std::strtok;
using std::strcat;
using std::strcpy;
void printPigLatin( char * );
int main()
{
char sentence[500];
char *token;
cout << "Enter string to tokenize and convert: ";
cin.getline( sentence, 500 );
token = strtok( sentence, " " );
cout << "\nPig latin for each token will be: " << endl;
while( token != NULL )
{
printPigLatin( token );
token = strtok( NULL, " " );
}
return 0;
}
void printPigLatin( char *word )
{
char temp[50];
for( int i = 0; *word != '\0'; i++ )
{
temp[i] = word[i + 1];
}
strcat( temp, "ay" );
cout << temp << endl;
}
I understand the tokenizing part quite clearly but I'm not sure how to do the pig latin.. i tried to start by simply adding "ay" to the token and see what the results will be .. not sure why the program goes into an infinite loop and keeps on displaying "ayay" .. any tips?
EDIT: this one works fine now but im not sure how to add the first letter of the token before adding the "ay"
EDIT: this is how i "see" it done but not sure how to correctly implement it ..
You're running over your input string with strcat. You need to either create a new string for each token, copying the token and "ay", or simply print the token and then "ay". However, if you're using C++ why not use istream iterators and STL algorithms?
To be honest, I severly doubt the quality of the C++ book, judging from your example. The “basic stuff” in C++ isn't the C pointer style programming. Rather, it's applying high-level library functionality. As “On Freund” pointed out, the C++ standard library provides excellent features to tackle your task. You might want to search for recommendations of better C++ books.
Concerning the problem: your printPigLatin could use the existing function strcpy (or better: strncpy which is safer in regards to buffer overflows). Your manual copy omits the first character from the input because you're using the i + 1st position. You also have a broken loop condition which always tests the same (first) character. Additionally, this should result in an overflow anyway.
As the people before me pointed out, there are several other methods of achieving what you want to do.
However, the actual problem with your code seems to be the use of strcat, I see that you changed it a bit in the edit. Here is an explanation of why the initial one did not work char* and size issues
Basically, the pointer does not allocate enough memory to add the "ay" to the string provided. If you create a pointer using the technique shown in the link, it should work fine.
I got your program to work, taking the strcat out and using
cout << word << "ay" << endl
Your loop is infinite because of *word != '\0'.
The word pointer is not changed at any time in the loop.
This seemed to have worked:
void printPigLatin( char *word )
{
cout << word + 1 << word[0] << "ay" << endl;
}
Just not sure if it's a good idea to do that.