I want to compare output of stringstream with some string.
Problem is when I use fill and width on stringstream I cant compare resulting string with preloaded string.
std::stringstream sstr;
sstr.fill(' ');
sstr.width(4);
sstr << 4 << std::endl;
if(" 4" == sstr.str()){
std::cout << "Equal" << std::endl;
}
It's not equal. My educated guess would be that width somehow use some kind of flag or other kind of indicator to replace bunch of spaces in string. But I am not sure and didn't find anything useful on google. Does anyone know why I cannot compare that (sstream.str() and targeted string)?
Goal is to test what will stringstream (which is heart of my component) print on console.
You also inserted a std::endl into the string. That's going to add a newline character to the string.
Remove the std::endl from your output.
Related
I am fairly new to programming and would like help with my homework. I have no idea where to even start.
"
1. Have the user input a sentence
2. Print out the individual words in the sentence, along with the word number
So the string "This is a test of our program." should produce:
1. This
2. is
3. a
4. test
5. of
6. our
7. program
This should strip out all spaces, commas, periods, exclamation points."
if you can give me some pointers. thanks.
You will have to use strings and streams from the standard library. You can start by including the following headers
#include <string>
#include <iostream>
A good starting point would be to look at the introduction here
Try some stuff with std::cout. This method allows you to output content to the console. Start with something easy, such as:
std::cout << "Hello World" << endl;
You can also output the content of a variable the same way:
std::string myString = "SomeText";
std::cout << myString << endl;
std::cout does the opposite. It allows you to capture the user input into a variable.
int myNumber;
std::cin >> myNumber;
or
std::string userInputString;
std::getline(std::cin, userInputString)
Notice that in the second case we're using std::getline. This is because std::cin behaves in such a way that it will stop after the first word if you write an entire sentence.
Now that you've captured the user input string, you can remove undesired characters, split the string, etc.. Look at what is available in the string class. Good luck.
Currently I only know of two methods to insert values into a C++ string or C string.
The first method I know of is to use std::sprintf() and a C-string buffer (char array).
The second method is to use something like "value of i: " + to_string(value) + "\n".
However, the first one needs the creation of a buffer, which leads to more code if you just want to pass a string to a function. The second one produces long lines of code, where a string gets interrupted every time a value is inserted, which makes the code harder to read.
From Python I know the format() function, which is used like this:
"Value of i: {}\n".format(i)
The braces are replaced by the value in format, and further .format()'s can be appended.
I really like Python's approach on this, because the string stays readable, and no extra buffer needs to be created. Is there any similar way of doing this in C++?
Idiomatic way of formatting data in C++ is with output streams (std::ostream reference). If you want the formatted output to end up in a std::string, use an output string stream:
ostringstream res;
res << "Value of i: " << i << "\n";
Use str() member function to harvest the resultant string:
std::string s = res.str();
This matches the approach of formatting data for output:
cout << "Value of i: " << i << "\n";
I'm struggling with the following: I'm reading from an XML file the following std::stringstream
"sigma=0\nreset"
Which after some copying&processing is written to a text-file. And I was hoping for the following
sigma=0
reset
But sadly I only get
sigma=0\nreset
but when I directly stream
out << "sigma=0\nreset"
I get:
sigma=0
reset
I currently suspect that some qualifier of the "\n" is lost during the "copy&processing"... is this possible? How to track down a "\n" in the stream which isn't a linefeed anymore?
Thank you!
It's because the output functions doesn't handle the escape sequences like '\n', it's the compiler that does and then only for literals. The compiler knows nothing of the contents of strings, and so can not do the translation "\n" to newline when inside a string.
You have to parse the string itself, and write out newlines when appropriate.
Assuming that the std::stringstream actually contains what is equivalent to the literal "sigma=0\\nreset" (length = 14 characters) and not "sigma=0\nreset" (length = 13 characters), you'll have to replace it yourself. Doing so is not very difficult, either use boost's replace_all (http://www.boost.org/doc/libs/1_53_0/doc/html/boost/algorithm/replace_all.html), or std::string::find and std::string::replace:
std::stringstream inStream;
inStream.str ("sigma=0\\nreset");
std::string content = inStream.str();
size_t index = content.find("\\n",0);
while(index != std::string::npos)
{
content.replace(index, 2, "\n");
index = content.find("\\n",index);
}
std::cout << content << '\n';
Note: you may want to consider cases when the system end-of-line is something other than "\n"
If the std::stringstream actually contains "sigma=0\nreset", then please post the code that does the copying/processing and the writing to the text file.
We're seeing a strange scenario that basically boils down to the following:
std::string something = "someval";
std::stringstream s;
s << something;
std::cout << s.str();
is not equal to:
std::string something = "someval";
std::stringstream s;
s << something.c_str();
std::cout << s.str();
Taking that a step farther - the output is not gibberish in either case. What is happening is the output from case 1 appears to be mapped to another (valid) string in the system whereas the output from case 2 is what is expected.
We see this behavior by simply changing:
s << something;
To:
s << something.c_str();
I know this sounds crazy (or it does to me), and I haven't been able to replicate it out of the larger system - so sorry for no "working" example. But does anyone know how this kind of thing can happen? Can we be stepping on memory somewhere or doing something to a stringtable in some location or anything else like that?
It is different if the string contains nul characters, '\0'.
The .c_str() version will compute the length up to the nul, while the std::string output will know its length and output all its characters.
I am new to C++ (coming from a C# background) and am trying to learn how to convert a string to an int.
I got it working by using a stringstream and outputting it into a double, like so:
const char* inputIndex = "5+2";
double number = 0;
stringstream ss(inputIndex);
ss >> number;
// number = 5
This works great. The problem I'm having is that the strings I'm parsing start with a number, but may have other, not digit characters after the digits (e.g. "5+2", "9-(3+2)", etc). The stringstream parses the digits at the beginning and stops when it encounters a non-digit, like I need it to.
The problem comes when I want to know how many characters were used to parse into the number. For example, if I parse 25+2, I want to know that two characters were used to parse 25, so that I can advance the string pointer.
So far, I got it working by clearing the stringstream, inputting the parsed number back into it, and reading the length of the resulting string:
ss.str("");
ss << number;
inputIndex += ss.str().length();
While this does work, it seems really hacky to me (though that might just be because I'm coming from something like C#), and I have a feeling that might cause a memory leak because the str() creates a copy of the string.
Is there any other way to do this, or should I stick with what I have?
Thanks.
You can use std::stringstream::tellg() to find out the current get position in the input stream. Store this value in a variable before you extract from the stream. Then get the position again after you extract from the stream. The difference between these two values is the number of characters extracted.
double x = 3435;
std::stringstream ss;
ss << x;
double y;
std::streampos pos = ss.tellg();
ss >> y;
std::cout << (ss.tellg() - pos) << " characters extracted" << std::endl;
The solution above using tellg() will fail on modern compilers (such as gcc-4.6).
The reason for this is that tellg() really shows the position of the cursor, which is now out of scope. See eg "file stream tellg/tellp and gcc-4.6 is this a bug?"
Therefore you need to also test for eof() (meaning the entire input was consumed).