Does “cin†reset variable to some default value if input type differs from destination type? [duplicate]
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Why does stringstream >> change value of target on failure?
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I have an issue with behavior of "cin" (I do not understand). My IDE is Netbeans under Windows OS (with Cygwin).
Here's a code example:
int main()
int temp = -1;
std::cin >> temp; // here user enters string of characters (string) or a single character
if (temp == 0)
std::cout << "temp = " << temp << ".n";
if (temp == -1)
std::cout << "temp = " << temp << ".n";
return 0;
This code shows message temp = 0 if I enter some sort of a character/string of characters. It's like there is conversion of char to int and conversion always ending by value 0.
Thank you if you can explain this behavior.
c++ cin
edited Aug 16 at 8:52
Toby Speight
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asked Aug 16 at 6:59
RickSanch3z
676
marked as duplicate by NathanOliver c++
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Aug 16 at 13:41
This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.
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up vote
10
down vote
favorite
This question already has an answer here:
Why does stringstream >> change value of target on failure?
2 answers
I have an issue with behavior of "cin" (I do not understand). My IDE is Netbeans under Windows OS (with Cygwin).
Here's a code example:
int main()
int temp = -1;
std::cin >> temp; // here user enters string of characters (string) or a single character
if (temp == 0)
std::cout << "temp = " << temp << ".n";
if (temp == -1)
std::cout << "temp = " << temp << ".n";
return 0;
This code shows message temp = 0 if I enter some sort of a character/string of characters. It's like there is conversion of char to int and conversion always ending by value 0.
Thank you if you can explain this behavior.
c++ cin
edited Aug 16 at 8:52
Toby Speight
14.7k133660
asked Aug 16 at 6:59
RickSanch3z
676
marked as duplicate by NathanOliver c++
Users with the  c++ badge can single-handedly close c++ questions as duplicates and reopen them as needed.
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Aug 16 at 13:41
This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.
The input thatstd::cinreads is a stream of text. Beyond that, it does not have a type. The extractor (operator>>) converts that text into a value of the appropriate type if it can.
– Pete Becker
Aug 16 at 12:53
add a comment |Â
up vote
10
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favorite
up vote
10
down vote
favorite
This question already has an answer here:
Why does stringstream >> change value of target on failure?
2 answers
I have an issue with behavior of "cin" (I do not understand). My IDE is Netbeans under Windows OS (with Cygwin).
Here's a code example:
int main()
int temp = -1;
std::cin >> temp; // here user enters string of characters (string) or a single character
if (temp == 0)
std::cout << "temp = " << temp << ".n";
if (temp == -1)
std::cout << "temp = " << temp << ".n";
return 0;
This code shows message temp = 0 if I enter some sort of a character/string of characters. It's like there is conversion of char to int and conversion always ending by value 0.
Thank you if you can explain this behavior.
c++ cin
edited Aug 16 at 8:52
Toby Speight
14.7k133660
asked Aug 16 at 6:59
RickSanch3z
676
This question already has an answer here:
Why does stringstream >> change value of target on failure?
2 answers
I have an issue with behavior of "cin" (I do not understand). My IDE is Netbeans under Windows OS (with Cygwin).
Here's a code example:
int main()
int temp = -1;
std::cin >> temp; // here user enters string of characters (string) or a single character
if (temp == 0)
std::cout << "temp = " << temp << ".n";
if (temp == -1)
std::cout << "temp = " << temp << ".n";
return 0;
This code shows message temp = 0 if I enter some sort of a character/string of characters. It's like there is conversion of char to int and conversion always ending by value 0.
Thank you if you can explain this behavior.
This question already has an answer here:
Why does stringstream >> change value of target on failure?
2 answers
c++ cin
edited Aug 16 at 8:52
Toby Speight
14.7k133660
asked Aug 16 at 6:59
RickSanch3z
676
edited Aug 16 at 8:52
Toby Speight
14.7k133660
edited Aug 16 at 8:52
Toby Speight
14.7k133660
edited Aug 16 at 8:52
Toby Speight
14.7k133660
14.7k133660
asked Aug 16 at 6:59
RickSanch3z
676
asked Aug 16 at 6:59
RickSanch3z
676
asked Aug 16 at 6:59
RickSanch3z
676
676
marked as duplicate by NathanOliver c++
Users with the  c++ badge can single-handedly close c++ questions as duplicates and reopen them as needed.
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Aug 16 at 13:41
This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.
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Aug 16 at 13:41
This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.
The input thatstd::cinreads is a stream of text. Beyond that, it does not have a type. The extractor (operator>>) converts that text into a value of the appropriate type if it can.
– Pete Becker
Aug 16 at 12:53
add a comment |Â
The input thatstd::cinreads is a stream of text. Beyond that, it does not have a type. The extractor (operator>>) converts that text into a value of the appropriate type if it can.
– Pete Becker
Aug 16 at 12:53
The input that
std::cin reads is a stream of text. Beyond that, it does not have a type. The extractor (operator>>) converts that text into a value of the appropriate type if it can.– Pete Becker
Aug 16 at 12:53
The input that
std::cin reads is a stream of text. Beyond that, it does not have a type. The extractor (operator>>) converts that text into a value of the appropriate type if it can.– Pete Becker
Aug 16 at 12:53
add a comment |Â
2 Answers
2
active
oldest
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up vote
18
down vote
accepted
This is expected behavior of std::basic_istream::operator>>; since C++11 if extraction fails, the variable will be set to 0. Before C++11, the variable won't be modified then its original value remains.
If extraction fails (e.g. if a letter was entered where a digit is
expected), value is left unmodified and failbit is set. (until C++11)
If extraction fails, zero is written to value and failbit is set. If
extraction results in the value too large or too small to fit in
value, std::numeric_limits::max() or std::numeric_limits::min()
is written and failbit flag is set. (since C++11)
answered Aug 16 at 7:02
songyuanyao
83.6k9161219
1
If no characters could be read then the value is unchanged; the setting 0 only happens on conversion failure
– M.M
Aug 16 at 9:12
2
Just for information: I've usedstd::cin.fail()to check if there a failbit set.
– RickSanch3z
Aug 16 at 9:39
add a comment |Â
up vote
4
down vote
If the read fails operator>> will set the value to zero (cppreference):
If extraction fails, zero is written to value and failbit is set.
answered Aug 16 at 7:02
vitaut
21.6k1187148
add a comment |Â
2 Answers
2
active
oldest
votes
2 Answers
2
active
oldest
votes
active
oldest
votes
active
oldest
votes
up vote
18
down vote
accepted
This is expected behavior of std::basic_istream::operator>>; since C++11 if extraction fails, the variable will be set to 0. Before C++11, the variable won't be modified then its original value remains.
If extraction fails (e.g. if a letter was entered where a digit is
expected), value is left unmodified and failbit is set. (until C++11)
If extraction fails, zero is written to value and failbit is set. If
extraction results in the value too large or too small to fit in
value, std::numeric_limits::max() or std::numeric_limits::min()
is written and failbit flag is set. (since C++11)
answered Aug 16 at 7:02
songyuanyao
83.6k9161219
1
If no characters could be read then the value is unchanged; the setting 0 only happens on conversion failure
– M.M
Aug 16 at 9:12
2
Just for information: I've usedstd::cin.fail()to check if there a failbit set.
– RickSanch3z
Aug 16 at 9:39
add a comment |Â
up vote
18
down vote
accepted
This is expected behavior of std::basic_istream::operator>>; since C++11 if extraction fails, the variable will be set to 0. Before C++11, the variable won't be modified then its original value remains.
If extraction fails (e.g. if a letter was entered where a digit is
expected), value is left unmodified and failbit is set. (until C++11)
If extraction fails, zero is written to value and failbit is set. If
extraction results in the value too large or too small to fit in
value, std::numeric_limits::max() or std::numeric_limits::min()
is written and failbit flag is set. (since C++11)
answered Aug 16 at 7:02
songyuanyao
83.6k9161219
1
If no characters could be read then the value is unchanged; the setting 0 only happens on conversion failure
– M.M
Aug 16 at 9:12
2
Just for information: I've usedstd::cin.fail()to check if there a failbit set.
– RickSanch3z
Aug 16 at 9:39
add a comment |Â
up vote
18
down vote
accepted
up vote
18
down vote
accepted
This is expected behavior of std::basic_istream::operator>>; since C++11 if extraction fails, the variable will be set to 0. Before C++11, the variable won't be modified then its original value remains.
If extraction fails (e.g. if a letter was entered where a digit is
expected), value is left unmodified and failbit is set. (until C++11)
If extraction fails, zero is written to value and failbit is set. If
extraction results in the value too large or too small to fit in
value, std::numeric_limits::max() or std::numeric_limits::min()
is written and failbit flag is set. (since C++11)
answered Aug 16 at 7:02
songyuanyao
83.6k9161219
This is expected behavior of std::basic_istream::operator>>; since C++11 if extraction fails, the variable will be set to 0. Before C++11, the variable won't be modified then its original value remains.
If extraction fails (e.g. if a letter was entered where a digit is
expected), value is left unmodified and failbit is set. (until C++11)
If extraction fails, zero is written to value and failbit is set. If
extraction results in the value too large or too small to fit in
value, std::numeric_limits::max() or std::numeric_limits::min()
is written and failbit flag is set. (since C++11)
answered Aug 16 at 7:02
songyuanyao
83.6k9161219
edited Aug 16 at 7:16
answered Aug 16 at 7:02
songyuanyao
83.6k9161219
answered Aug 16 at 7:02
songyuanyao
83.6k9161219
answered Aug 16 at 7:02
songyuanyao
83.6k9161219
83.6k9161219
1
If no characters could be read then the value is unchanged; the setting 0 only happens on conversion failure
– M.M
Aug 16 at 9:12
2
Just for information: I've usedstd::cin.fail()to check if there a failbit set.
– RickSanch3z
Aug 16 at 9:39
add a comment |Â
1
If no characters could be read then the value is unchanged; the setting 0 only happens on conversion failure
– M.M
Aug 16 at 9:12
2
Just for information: I've usedstd::cin.fail()to check if there a failbit set.
– RickSanch3z
Aug 16 at 9:39
1
1
If no characters could be read then the value is unchanged; the setting 0 only happens on conversion failure
– M.M
Aug 16 at 9:12
If no characters could be read then the value is unchanged; the setting 0 only happens on conversion failure
– M.M
Aug 16 at 9:12
2
2
Just for information: I've used
std::cin.fail() to check if there a failbit set.– RickSanch3z
Aug 16 at 9:39
Just for information: I've used
std::cin.fail() to check if there a failbit set.– RickSanch3z
Aug 16 at 9:39
add a comment |Â
up vote
4
down vote
If the read fails operator>> will set the value to zero (cppreference):
If extraction fails, zero is written to value and failbit is set.
answered Aug 16 at 7:02
vitaut
21.6k1187148
add a comment |Â
up vote
4
down vote
If the read fails operator>> will set the value to zero (cppreference):
If extraction fails, zero is written to value and failbit is set.
answered Aug 16 at 7:02
vitaut
21.6k1187148
add a comment |Â
up vote
4
down vote
up vote
4
down vote
If the read fails operator>> will set the value to zero (cppreference):
If extraction fails, zero is written to value and failbit is set.
answered Aug 16 at 7:02
vitaut
21.6k1187148
If the read fails operator>> will set the value to zero (cppreference):
If extraction fails, zero is written to value and failbit is set.
answered Aug 16 at 7:02
vitaut
21.6k1187148
answered Aug 16 at 7:02
vitaut
21.6k1187148
answered Aug 16 at 7:02
vitaut
21.6k1187148
answered Aug 16 at 7:02
vitaut
21.6k1187148
21.6k1187148
add a comment |Â
add a comment |Â
The input that
std::cinreads is a stream of text. Beyond that, it does not have a type. The extractor (operator>>) converts that text into a value of the appropriate type if it can.– Pete Becker
Aug 16 at 12:53