C++ Question.
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In the use of
string str;
getline(cin, str); // data gets entered here
if(str=="???" || str=="")
{
// invalid string
}
else
{
// VALID string
}The logic is always executing the invalid string segment, even when valid data is entered. Why is this happening? Thanks for any insight. :) William Fortes in fide et opere!
Try using
strcmp(). I've had problems trying to use normal logical operators on strings andchararrays before but using the different compare functions sure saved me from headaches. The question "Do computers think?" is the same as "Can submarines swim?" DragonFire Software Jeryth -
Mr.Prakash wrote: what kinda of comparison is (str=="???") no one compares like this to test wheather the string holds a valid data or not. When you do more than one comparions like this you need to put them inside parenthesis. The compiler should even report an error or warning. Mr.Prakash wrote: this string should be initialised to zero or null before reading... He uses
std::string, that string gets empty when it gets constructed. Rickard Andersson Here is my card, contact me later! UIN: 50302279 Sonork: 37318 -
Works OK for me in VC++ 6. Kevin
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Try using
strcmp(). I've had problems trying to use normal logical operators on strings andchararrays before but using the different compare functions sure saved me from headaches. The question "Do computers think?" is the same as "Can submarines swim?" DragonFire Software JerythThanks for your reply. Because I've worked with 'string' so often, and have equally studied its syntaxes and member functions in the C++ Standard library so much as well, I can say that the authors of 'string' went above and beyond their call of duty to make it as robust as possible. Not only is this reflected in the ways they have tried to make it as seamless for backward compatibility when dealing with C-Style 'char*' string, but they have sought to expand it with features that the old C-Style string did not possess. For example, the C++ Standard has overloaded the string comparison operators to accept three different kinds of comparisons when comparing std::strings. 1) a std::string with another std::string 2) a std::string with a C-Style char* cstr 3) a C-Style char* cstr with a std::string Those operators represent, ==, !=, <, >, <=, and >=. So there is no need to use the old C-Style 'strcmp' or 'strncmp' functions (which deals specifically with C-Style char* strings) when working with std::string. I believe the problem I'm experiencing, has more to do with 'getline()' than with 'strings'. I've had so many problems in the past using 'getline()', that I shun it like the plague. It's a beast of its own kind that seems to operate like a renegade. It might have good qualities, but (for me) it doesn't seem to be very lending. :sigh: William Fortes in fide et opere!
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Strange! because I have VC++ 6, and I tried a dozen or more different techniques before posting the question, and I couldn't get any of them produce the desired behavior. :confused: William Fortes in fide et opere!
Hmmm. I'm puzzled then. I think my VC++ has SP3 applied. perhaps that makes a difference? And I tried it on NT4. Kevin
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Hmmm. I'm puzzled then. I think my VC++ has SP3 applied. perhaps that makes a difference? And I tried it on NT4. Kevin
Thanks for your reply. Even stranger! that you have VC++ 6, SP3 and claim it works for you, while I with VC++ 6, SP5, cannot get the kind of behavior I'm looking for. The problem (it looks more and more to be), is that 'getline() isn't receiving any data from the input queue, because a 'cout' of the string (which is the input buffer) reveals NOTHING in it. Consequently, when the test is made to see if data is absent, the test succeeds because NO data has been collected and is the reason why the invalid segment gets activated. So the problem doesn't seem to rest with 'string', but more with 'getline()'. To be honest with you, 'getline()' has been a problem child for me every time I try to use it, and this time is no exception. :sigh: William Fortes in fide et opere!
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In the use of
string str;
getline(cin, str); // data gets entered here
if(str=="???" || str=="")
{
// invalid string
}
else
{
// VALID string
}The logic is always executing the invalid string segment, even when valid data is entered. Why is this happening? Thanks for any insight. :) William Fortes in fide et opere!
There is a known bug in the getline() VC 6.0 version (see MS KB #240015). This KB article has a "fix" which requires editing the string header file. It may not be related to the problem your having, but underscores your suspicions of getline(). By the way, it executes as expected in VS.NET 2003 without revision. Regards Mike
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There is a known bug in the getline() VC 6.0 version (see MS KB #240015). This KB article has a "fix" which requires editing the string header file. It may not be related to the problem your having, but underscores your suspicions of getline(). By the way, it executes as expected in VS.NET 2003 without revision. Regards Mike
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Strange! because I have VC++ 6, and I tried a dozen or more different techniques before posting the question, and I couldn't get any of them produce the desired behavior. :confused: William Fortes in fide et opere!
I dont understand why the comparison with three "?" is it a desired input?? or is it the comparison for uninitialised junk string? The World is getting smaller and so are the people.
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There is a known bug in the getline() VC 6.0 version (see MS KB #240015). This KB article has a "fix" which requires editing the string header file. It may not be related to the problem your having, but underscores your suspicions of getline(). By the way, it executes as expected in VS.NET 2003 without revision. Regards Mike
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In the use of
string str;
getline(cin, str); // data gets entered here
if(str=="???" || str=="")
{
// invalid string
}
else
{
// VALID string
}The logic is always executing the invalid string segment, even when valid data is entered. Why is this happening? Thanks for any insight. :) William Fortes in fide et opere!
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Move the cin, e.g. char line[100]; cout << " Type a line terminated by 't'" << endl; cin.getline( line, 100, 't' ); cout << line;
Thanks for replying. Your suggestion has merit to it (perhaps) for a number of other situations, but for what I'm doing, unless I can engender a character (other than any printable character), using a special terminating character (as this form of 'getline()' requires) would not work for me. For example, if I were to use "t" as my terminating character, there could very well be instances where I might need "t" as a single character to be by itself, which means when the 'getline()' function sees a single "t" standing by itself, it would interpret that single "t" as the terminating character and transfer the collected data from the input queue to the buffer, when in truth and fact, in that particular instance I did not mean for "t" to be a terminating character (it may have been meant to be data). This is especially true when dealing with scientific equations and formulas. :sigh: William Fortes in fide et opere!
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Thanks for replying. Your suggestion has merit to it (perhaps) for a number of other situations, but for what I'm doing, unless I can engender a character (other than any printable character), using a special terminating character (as this form of 'getline()' requires) would not work for me. For example, if I were to use "t" as my terminating character, there could very well be instances where I might need "t" as a single character to be by itself, which means when the 'getline()' function sees a single "t" standing by itself, it would interpret that single "t" as the terminating character and transfer the collected data from the input queue to the buffer, when in truth and fact, in that particular instance I did not mean for "t" to be a terminating character (it may have been meant to be data). This is especially true when dealing with scientific equations and formulas. :sigh: William Fortes in fide et opere!
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Then simply use: cin.getline( line, 100) for the example given. The DEFAULT will be '\n' (carriage return) added as the final character when the return (enter) key is pressed.
In case you haven't been reading the other posts, 'getline()' has a bug in it, and is unfit to use (at least for VC++ 6). Even the fix that MS has issued, DOES NOT WORK!! Take my word for it, I am very acquainted with the various iostream member functions (including 'getline()') and the only reason why I posted the question on this forum, was in hope that somebody may have found a workaround for the problems this I/O function has been plagued with. I understand VC++ 7 does not have this problem, and that is good news for those who might want to use it. :suss: William Fortes in fide et opere!
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In the use of
string str;
getline(cin, str); // data gets entered here
if(str=="???" || str=="")
{
// invalid string
}
else
{
// VALID string
}The logic is always executing the invalid string segment, even when valid data is entered. Why is this happening? Thanks for any insight. :) William Fortes in fide et opere!
I have 6.00 and works fine for me, try this out: #include "stdafx.h" #include "iostream.h" #include "string.h" int main(int argc, char* argv[]) { char line[100]; cout << "Type a line" << endl; cin.getline( line, 100); if(strcmp(line, "xxx") == 0) cout << "You entered xxx"; else cout << "You did not enter xxx"; return 0; }
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In the use of
string str;
getline(cin, str); // data gets entered here
if(str=="???" || str=="")
{
// invalid string
}
else
{
// VALID string
}The logic is always executing the invalid string segment, even when valid data is entered. Why is this happening? Thanks for any insight. :) William Fortes in fide et opere!
Doing it the way you have you have to press the enter key twice after getline to get a response (the bug you were referring to). See http://support.microsoft.com/default.aspx?scid=kb;en-us;Q240015 for the fix ( the fix does work if you make the changes in the right file. The file referred to is in two different locations. You might as well change the code in both: MicrosoftVisualStudio\VC98\Include\String and MicrosoftVisualStudio\VC98\CRT\SRC\String I did and the enter key only has to be pressed once now and the code below which is like your way of doing it works fine. #include "stdafx.h" #include "string" #include "iostream" using namespace std ; int main(int argc, char* argv[]) { string s1; cout << "Enter a sentence:"; getline(cin,s1); if(s1 == "???" || s1 == "") cout << "First case"; else cout << "Second case"; return 0; }