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Questions tagged [istream]

In C++ std::istream is the base class for input streams.

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How to block on reading a c++ stringstream to wait for data

So, I've been trying to figure out, how to wait for data from a C++ stringstream (for instance), without being constantly checking if data is there, which is quite CPU consuming. I'm perfectly able to read, for instance, from a serial device, and…
cvicente
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Is this a bug with getline(), or am I doing something wrong. Right way to use getline()?

It might not be a bug, but I don't know what is going wrong. My first entry is repeated for str1 on 2nd iteration, and is same way from then. Only first iteration goes good. #include #include using namespace std; int main ()…
ani
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Is it guaranteed that std::char_traits::to_int_type(c) == static_cast(c)?

The question How to use correctly the return value from std::cin.get() and std::cin.peek()? made me wonder if it is guaranteed that std::char_traits::to_int_type(c) == static_cast(c) for all valid char values c. This comes up in a lot…
L. F.
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What is an istream_view and when do I use one?

Apparently, C++20 has a new std::istream-related construct: std::istream_view. The cppreference page on it is a stub right now†. So, what is a "view of an istream" and what can I use it for? † - Ok, technically it redirects to a page about…
einpoklum
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why does a blank line occupy to two bytes?

I'm new to C++. I'd like to count the blank lines at the end of a text file. But now i meet a problem. The contents of the text file are like: test.txt 1 2 blank line The code is: #include #include using namespace std; int…
Oliver Yu
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Is it always safe to use std::istream::peek()?

I usually teach my students that the safe way to tackle file input is: while (true) { // Try to read if (/* failure check */) { break; } // Use what you read } This saved me and many people from the classical and most of the…
Costantino Grana
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Handling invalid input in input stream operator >>

What is the recommended (standard) way of handling invalid input in extraction operator: std::istream& operator>>(std::istream& is, SomeType& val) { // ... return is; } Should it set std::ios_base::failbit and return immediately? Is it okay…
trozen
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insert a string in front of a istream in cpp

My problem is something like I want to append some string in front of a iostream. You can say in front of std::cin. #include #include void print(std::istream & in){// function not to be modified std::string str; in >>…
keen_learner
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istream's tellg/seekg cannot be protected from stack smashing (g++)?

For a program that I'm writing, it is useful for me to calculate file sizes, which I calculate by using iostream's tellg and seekg functions, but this leads to a warning by -Wstack-protector. The following code reproduces the "problem": #include…
Zorawar
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.NET equivalent of Delphi IStream initialization

I have the following Delphi code: var Stream: TMemoryStream; StreamI: TStreamAdapter; OleStream: IStream; begin Stream:= TMemoryStream.Create; Stream.LoadFromFile(filename); StreamI:= TStreamAdapter.Create(Stream, soOwned); …
SharpAffair
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C++ common interface for "cin" and "File"

Is there a common interface for cin and file input? I want to make a program that has an optional parameter prog [input-file] If an input file is specified, then it should read from the file, and if not, it should read from cin. From what I can…
Verhogen
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Why `s.clear(ios::badbit);` below? Why not `s.clear(ios::failbit);`?

I was looking into this question and I have no problem understanding the two answers given to it. But I'm not sure I understood the s.clear(ios::badbit); in the statement highlighted below with the comment // set state. For instance, why not…
John Kalane
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Reading in one byte at a time with .get()

So i'm reading in a input file that contains: lololololololol I need to read it in using binary one byte at a time for something I'm doing later on. To do this i'm using get() to read it in then storing it into a char. It seems to be working…
David Dennis
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istream with popen functionality

I have a function that accepts istream class. I need to be able to make it work with gzip data. Is there in C++ standard istream-like class with popen()-like functionality? Alternatively, is there a way to convert FILE * to istream?
Nick
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Using cin for keyboard input after processing redirected file input with getline

I know, this question has been treated tons of times.. but I can't make it work anyway.. here I paste some code: #include #include "header.h" using namespace std; using namespace header; int main(){ string parent, child, line, node; …
Moriduri
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