I'm trying to print 3 attributes from a struct. Why won't they all print? They will print 2 at a time, but not all three together.
name has a Carriage Return character at the end. So it's printing
2HP Potion\r10
\r moves the cursor to the beginning of the line, without moving to the next line, so 10 overwrites 2H.
I suspect this is because you read the name from a file that was written on Windows, which uses \r\n as its line break sequence in text files. You should either fix the file using dos2unix, or change the code that reads the file to remove \r characters.
You can remove the \r at the end with:
int last_pos = name.size()-1;
if (last_pos >= 0 && name[last_pos] == '\r') {
name.pop_back();
}
Related
In the following program, if I use the line for the negated scanset, it works fine if I enter a multi-word line (ending with ENTER or newline), even though the newline is in the negated list.
But if I use the line for the scanset instead and enter the word "aegis" (or any word with consonants for that matter), then junk characters are output. Analogous to the first case, shouldn't at least "ae" be output if I enter this word? Please explain this behavior of scanset and negated scanset for scanf().
#include <stdio.h>
int main ()
{
char str[30];
printf("Enter the string\n");
//scanf("%[^\n]",str);
//scanf("%[aeiou]",str);
printf("%s",str);
}
It is because code errantly does not check the return value of scanf()
printf("Enter the string\n");
scanf("%[^\n]",str);
scanf("%[aeiou]",str); // check result before using `str`
printf("%s",str);
With scanf("%[^\n]",str); and input like "123\n", str get the values of "123" and '\n' remains in stdin. Then with scanf("%[aeiou]",str); and input like "aegis\n", the first line's '\n' blocks saving anything as '\n' is not a vowel, nothing is saved in str and since code did not check the return value of scanf(), does not realized that str may be invalid.
1) Always check the return value of scanf() and family.
if (scanf(some_format, var1, var2, ...) != ExpectedConversionCount) {
Fail();
}
2) scanf("%[^\n]",str); to read a line fails 3 things: No input limit, fails to read anything if the the line consists of only '\n'. Without check the return value, EOF is not detected.
3) Use fgets() instead of scanf() for user input.
I have written a c++ code for changing file formats. Part of the functionality is to add a configured line end character. For one of file conversions, the line end character required is "\r\n" i.e. CR+NL .
My code basically reads the configured value from DB and appends it to the end of each record. Something on the lines of
//read DB and store line end char in a string lets say lineEnd.
//code snippet for file writting
string record = "this is a record";
ofstream outFileStream;
string outputFileName = "myfile.txt";
outFileStream.open (outputFileName.c_str());
outFileStream<<record;
outFileStream<<lineEnd; // here line end contains "\r\n"
But this prints record followed by \r\n as it is, no translation to CR+NL takes place.
this is a record\r\n
While the following works (prints CR+LF in output file)
outFileStream<<record;
outFileStream<<"\r\n";
this is a record
But I can not hard code it. I am facing similar issues with "\n" also.
Any suggestions on how to do it.
The translation of \r into the ASCII character CR and of \n into the ASCII character LF is done by the compiler when parsing your source code, and in literals only. That is, the string literal "A\n" will be a 3-character array with values 65 10 0.
The output streams do not interpret escape sequences in any way. If you ask an output stream to write the characters \ and r after each other, it will do so (write characters with ASCII value 92 and 114). If you ask it to write the character CR (ASCII code 13), it will do so.
The reason std::cout << "\r"; writes the CR character is that the string literal already contains the character 13. So if your database includes the string \r\n (4 characters: \, \r, \, n, ASCII 92 114 92 110), that is also the string you will get on output. If it contained the string with ASCII 13 10, that's what you'd get.
Of course, if it's impractical for you to store 13 10 in the database, nothing prevents you from storing 92 114 92 110 (the string "\r\n") in there, and translating it at runtime. Something like this:
void translate(std::string &str, const std::string &from, const std:string &to)
{
std::size_t at = 0;
for (;;) {
at = str.find(from, at);
if (at == str.npos)
break;
str.replace(at, from.size(), to);
}
}
std::string lineEnd = getFromDatabase();
translate(lineEnd, "\\r", "\r");
translate(lineEnd, "\\n", "\n");
Aim: to read a string in the form First\nSecond from a file and to print it as
First
Second
Problem: if the string is defined in the code, as in line = "First\nSecond";, then it is printed on two lines; if instead I read it from a file then is printed as
First\nSecond
Short program illustrating the problem:
#include "stdafx.h" // I'm using Visual Studio 2008
#include <fstream>
#include <string>
#include <iostream>
void main() {
std::ifstream ParameterFile( "parameters.par" ) ;
std::string line ;
getline (ParameterFile, line) ;
std::cout << line << std::endl ;
line = "First\nSecond";
std::cout << line << std::endl ;
return;
}
The parameters.par file contains only the line
First\nSecond
The Win32 console output is
C:\blabla>SOtest.exe
First\nSecond
First
Second
Any suggestion?
In C/C++ string literals ("...") the backslash is used to mark so called "escape sequences" for special characters. The compiler translates (replaces) the two characters '\' (ASCII code 92) followed by 'n' (ASCII code 110) by the new-line character (ASCII code 10). In a text file one would normally just hit the [RETURN] key to insert a newline character. If you really need to process input containing the two characters '\' and 'n' and want to handle them like a C/C++ compiler then you must explicitely replace them by the newline character:
replace(line, "\\n", "\n");
where you have to supply a replace function like this:
Replace part of a string with another string (Standard C++ does not supply such a replace function by itself.)
Other escape sequences supported by C/C++ and similar compilers:
\t -> [TAB]
\" -> " (to distinguish from a plain ", which marks the end of a string literal, but is not part of the string itself!)
\\ -> \ (to allow having a backslash in a string literal; a single backslash starts an escape sequence)
The character indicated in a string literal by the escape sequence \n is not the same as the sequence of characters that looks like \n!
When you think you're assigning First\nSecond, you're not. In your source code, \n in a string literal is a "shortcut" for the invisible newline character. The string does not contain \n - it contains the newline character. It's automatically converted for you.
Whereas what you're reading from your file is the actual characters \ and n.
I have a problem, using fscanf function :(
I need to reed a sequence of characters from file like "a b c d" (characters are separated by space).
but it doesn't works :(
how I have to read them? (
I tried to print it and the result is uncorrect. I think, it's because of spaces. I really don't know why it doesn't work.
Tell me please, what is wrong with array access?
From cplusplus.com:
The function will read and ignore any whitespace characters encountered before the next non-whitespace character (whitespace characters include spaces, newline and tab characters -- see isspace). A single whitespace in the format string validates any quantity of whitespace characters extracted from the stream (including none).
Then if your code is:
while ( fscanf(fin,"%c", &array[i++]) == 1 );
and your file is like this:
h e l l o
Your array will be:
[h][ ][e][ ][l][ ][l][ ][o]
If you change your code into:
while ( fscanf(fin," %c", &array[i++]) == 1 );
with the same file your array will be:
[h][e][l][l][o]
In any case the code works: it depends on what you want.
Anyway, you should think about starting to use fgets() + sscanf(), for example:
char buff[NUM];
while ( fgets(buff, sizeof buff, fin) )
sscanf(buff,"%c", &array[i++]);
With the single fscanf() the lack of buffer management can turns into buffer overflow problems.
Add white space before %c =>
while (fscanf(pFile," %c", &alpArr[i++]) == 1);
It should work.
I have a text file made of 3 lines:
Line 1
Line 3
(Line 1, a blank line, and Line 3)
vector<string> text;
vector<string>::iterator it;
ifstream file("test.txt");
string str;
while (getline(file, str))
{
if (str.length() == 0)
str = "\n";
// since getline discards the newline character, replacing blank strings with newline
text.push_back(str);
} // while
for (it=text.begin(); it < text.end(); it++)
cout << (*it);
Prints out:
Line 1
Line 3
I'm not sure why the string with only a newline was not printed out. Any help would be appreciated. Thanks.
Wasn't? Actually, it was! The reason you have a newline after Line 1 is exactly that empty string with newline in it and nothing else. If not for that second line, you'd see Line 1Line 3 as output. (You said it yourself: getline discards newline characters.)
Apparently, the way I understand your intent, you were supposed to implement your output cycle as follows
for (it = text.begin(); it < text.end(); it++)
cout << *it << endl;
That way you add a newline after each string during output. But if so, then you don't need to manually add a \n character to empty strings during reading.
In other words, decide what is it you want to do. At this time it is not clear.
If you want to restore the discarded
newline characters during reading,
you have to do it for all lines,
not just for empty ones.
If you want to add the newline
characters during output, you don't
need to explictly push them into the
read lines at all.
In fact, it is a rather strange idea to literally push the newline characters into your strings. What for? Since you already read and store your text line-by-line, the newline characters can be implied. I.e. you can do the printing as I do it above (with endl), and everything will look as expected.
I think the simple answer here, is that getline() strips the trailing newline whether or not there is content in the string. So the three reads you do are as follows:
"Line 1"
""
"Line 3"
which you transform into:
"Line 1"
"\n"
"Line 3"
which when printed is:
Line 1
Line 3
I'd use something like this:
std::vector<std::string> text;
std::string str;
while (std::getline(infile, str))
text.push_back(str);
std::copy(text.begin(), text.end(),
std::ostream_iterator<std::string>(std::cout, "\n"));
You're adding complexity that stops your code from working.