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Using ternary operator in c++ returns false condition always [duplicate]

-2

This question already has an answer here:

• 
  How to compare two BSTRs or CComBSTRs?
  
  3 answers
  
  

I am using a statement with ternary operator which is always returning the other value.

BSTR pVal = L"Yes";

bool val = pVal == L"Yes" ? true : false;

this statement returns

 val = false;

I expect it to return true here. Am i making it wrong?

c++

share|improve this question

asked Mar 21 at 17:54

S.Frank RicharrdS.Frank Richarrd

1049

marked as duplicate by πάντα ῥεῖ c++
Users with the  c++ badge can single-handedly close c++ questions as duplicates and reopen them as needed.

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Mar 21 at 17:58

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.

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  BSTR types cannot be compared directly using ==.
  
  – πάντα ῥεῖ
  Mar 21 at 17:57
  

  
  
  
  


• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  
  Unrelated to your issue, but this is not a valid way to create a BSTR. They're supposed to be allocated with SysAllocString. In C++ it's best to use a wrapper type like _bstr_t, which will also solve your comparison issues.
  
  – interjay
  Mar 21 at 17:59
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  How to compare BSTR against a string
  
  – R Sahu
  Mar 21 at 18:00
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Not a bug, but a == b ? true : false is usually written a == b.
  
  – molbdnilo
  Mar 21 at 18:08
  

  
  
  
  

add a comment | 

-2

This question already has an answer here:

• 
  How to compare two BSTRs or CComBSTRs?
  
  3 answers
  
  

I am using a statement with ternary operator which is always returning the other value.

BSTR pVal = L"Yes";

bool val = pVal == L"Yes" ? true : false;

this statement returns

 val = false;

I expect it to return true here. Am i making it wrong?

c++

share|improve this question

asked Mar 21 at 17:54

S.Frank RicharrdS.Frank Richarrd

1049

marked as duplicate by πάντα ῥεῖ c++
Users with the  c++ badge can single-handedly close c++ questions as duplicates and reopen them as needed.

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Mar 21 at 17:58

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.

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  BSTR types cannot be compared directly using ==.
  
  – πάντα ῥεῖ
  Mar 21 at 17:57
  

  
  
  
  


• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  
  Unrelated to your issue, but this is not a valid way to create a BSTR. They're supposed to be allocated with SysAllocString. In C++ it's best to use a wrapper type like _bstr_t, which will also solve your comparison issues.
  
  – interjay
  Mar 21 at 17:59
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  How to compare BSTR against a string
  
  – R Sahu
  Mar 21 at 18:00
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Not a bug, but a == b ? true : false is usually written a == b.
  
  – molbdnilo
  Mar 21 at 18:08
  

  
  
  
  

add a comment | 

This question already has an answer here:

• 
  How to compare two BSTRs or CComBSTRs?
  
  3 answers
  
  

I am using a statement with ternary operator which is always returning the other value.

BSTR pVal = L"Yes";

bool val = pVal == L"Yes" ? true : false;

this statement returns

 val = false;

I expect it to return true here. Am i making it wrong?

c++

share|improve this question

asked Mar 21 at 17:54

S.Frank RicharrdS.Frank Richarrd

1049

BSTR pVal = L"Yes";

bool val = pVal == L"Yes" ? true : false;

 val = false;

share|improve this question

asked Mar 21 at 17:54

S.Frank RicharrdS.Frank Richarrd

1049

share|improve this question

asked Mar 21 at 17:54

S.Frank RicharrdS.Frank Richarrd

1049

asked Mar 21 at 17:54

S.Frank RicharrdS.Frank Richarrd

1049

asked Mar 21 at 17:54

S.Frank RicharrdS.Frank Richarrd

1049

1 Answer
1

active

oldest

votes

5

A lot here is wrong.

== on BSTR compares pointer values. Two L"Yes" being pointer-equal is implementation defined.

bool_expr?true:false is a noop.

bool val = wcscmp(pVal, L"Yes") == 0;

is probably what you want.

BSTR pVal = L"Yes";

is bad news; that isn't how you are supposed to create a BSTR. BSTR are supposed to be pascal-esque strings allocated in a specific region of memory.

BSTR pVal = SysAllocString(L"Yes");

is usually better.

Using wcscmp is valid on a BSTR, as BSTR is guaranteed null terminated. But assigning a null terminated string to a BSTR is not a good plan; the code consuming the BSTR may expect the length field to come before the first character.

It may even be a good plan to use _bstr_t which is a C++ wrapper around BSTR.

It is also usually a good idea to compare BSTR to BSTR and not using C APIs; a BSTR can contain embedded NULs, and C APIs stop at the first NUL.

_bstr_t pVal = L"Yes";

bool val = pVal == _bstr_t(L"Yes");

_bstr_t has an operator== that does a reasonable thing.

share|improve this answer

edited Mar 21 at 18:17

answered Mar 21 at 17:58

Yakk - Adam NevraumontYakk - Adam Nevraumont

188k21199384

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  bstr_t is a completely diferent type than wide string, one need to use the (Windows) OS conversion functions to convert one into another.
  
  – πάντα ῥεῖ
  Mar 21 at 18:00
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @πάνταῥεῖ Not completely different (you can use wcscmp), but yes, I added that.
  
  – Yakk - Adam Nevraumont
  Mar 21 at 18:03
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  You cannot safely use the C string functions. BSTRs can contain embedded NUL characters. They are Pascal-style strings, with the length stored inside the string. Not C-style strings with sentinel terminator characters.
  
  – Cody Gray♦
  Mar 21 at 18:09
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @CodyGray Part of that depends on what you want == to do, but yes, probably wrapping the other L"Yes" in a BSTR and using BSTR-approved comparisons is a good plan. On the other hand, I can guarantee I can find an issue with every single == on two strings; there are languages where multiple characters become fewer in other cases, combinations of characters codes that can be treated identically or not with other characters, etc.
  
  – Yakk - Adam Nevraumont
  Mar 21 at 18:15
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Yeah, just to be clear, it wasn't a criticism of your answer so much as a response to your discussion with πάντα in the comments. In this very limited case, where you're comparing to a string literal, it would obviously be fine to use wcscmp. I just wanted to explain why it's not a valid approach in general.
  
  – Cody Gray♦
  Mar 21 at 20:38
  
  

  
  
  
  

 | 
show 1 more comment

5

A lot here is wrong.

== on BSTR compares pointer values. Two L"Yes" being pointer-equal is implementation defined.

bool_expr?true:false is a noop.

bool val = wcscmp(pVal, L"Yes") == 0;

is probably what you want.

BSTR pVal = L"Yes";

is bad news; that isn't how you are supposed to create a BSTR. BSTR are supposed to be pascal-esque strings allocated in a specific region of memory.

BSTR pVal = SysAllocString(L"Yes");

is usually better.

Using wcscmp is valid on a BSTR, as BSTR is guaranteed null terminated. But assigning a null terminated string to a BSTR is not a good plan; the code consuming the BSTR may expect the length field to come before the first character.

It may even be a good plan to use _bstr_t which is a C++ wrapper around BSTR.

It is also usually a good idea to compare BSTR to BSTR and not using C APIs; a BSTR can contain embedded NULs, and C APIs stop at the first NUL.

_bstr_t pVal = L"Yes";

bool val = pVal == _bstr_t(L"Yes");

_bstr_t has an operator== that does a reasonable thing.

share|improve this answer

edited Mar 21 at 18:17

answered Mar 21 at 17:58

Yakk - Adam NevraumontYakk - Adam Nevraumont

188k21199384

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  bstr_t is a completely diferent type than wide string, one need to use the (Windows) OS conversion functions to convert one into another.
  
  – πάντα ῥεῖ
  Mar 21 at 18:00
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @πάνταῥεῖ Not completely different (you can use wcscmp), but yes, I added that.
  
  – Yakk - Adam Nevraumont
  Mar 21 at 18:03
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  You cannot safely use the C string functions. BSTRs can contain embedded NUL characters. They are Pascal-style strings, with the length stored inside the string. Not C-style strings with sentinel terminator characters.
  
  – Cody Gray♦
  Mar 21 at 18:09
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @CodyGray Part of that depends on what you want == to do, but yes, probably wrapping the other L"Yes" in a BSTR and using BSTR-approved comparisons is a good plan. On the other hand, I can guarantee I can find an issue with every single == on two strings; there are languages where multiple characters become fewer in other cases, combinations of characters codes that can be treated identically or not with other characters, etc.
  
  – Yakk - Adam Nevraumont
  Mar 21 at 18:15
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Yeah, just to be clear, it wasn't a criticism of your answer so much as a response to your discussion with πάντα in the comments. In this very limited case, where you're comparing to a string literal, it would obviously be fine to use wcscmp. I just wanted to explain why it's not a valid approach in general.
  
  – Cody Gray♦
  Mar 21 at 20:38
  
  

  
  
  
  

 | 
show 1 more comment

5

A lot here is wrong.

== on BSTR compares pointer values. Two L"Yes" being pointer-equal is implementation defined.

bool_expr?true:false is a noop.

bool val = wcscmp(pVal, L"Yes") == 0;

is probably what you want.

BSTR pVal = L"Yes";

is bad news; that isn't how you are supposed to create a BSTR. BSTR are supposed to be pascal-esque strings allocated in a specific region of memory.

BSTR pVal = SysAllocString(L"Yes");

is usually better.

Using wcscmp is valid on a BSTR, as BSTR is guaranteed null terminated. But assigning a null terminated string to a BSTR is not a good plan; the code consuming the BSTR may expect the length field to come before the first character.

It may even be a good plan to use _bstr_t which is a C++ wrapper around BSTR.

It is also usually a good idea to compare BSTR to BSTR and not using C APIs; a BSTR can contain embedded NULs, and C APIs stop at the first NUL.

_bstr_t pVal = L"Yes";

bool val = pVal == _bstr_t(L"Yes");

_bstr_t has an operator== that does a reasonable thing.

share|improve this answer

edited Mar 21 at 18:17

answered Mar 21 at 17:58

Yakk - Adam NevraumontYakk - Adam Nevraumont

188k21199384

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  bstr_t is a completely diferent type than wide string, one need to use the (Windows) OS conversion functions to convert one into another.
  
  – πάντα ῥεῖ
  Mar 21 at 18:00
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @πάνταῥεῖ Not completely different (you can use wcscmp), but yes, I added that.
  
  – Yakk - Adam Nevraumont
  Mar 21 at 18:03
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  You cannot safely use the C string functions. BSTRs can contain embedded NUL characters. They are Pascal-style strings, with the length stored inside the string. Not C-style strings with sentinel terminator characters.
  
  – Cody Gray♦
  Mar 21 at 18:09
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @CodyGray Part of that depends on what you want == to do, but yes, probably wrapping the other L"Yes" in a BSTR and using BSTR-approved comparisons is a good plan. On the other hand, I can guarantee I can find an issue with every single == on two strings; there are languages where multiple characters become fewer in other cases, combinations of characters codes that can be treated identically or not with other characters, etc.
  
  – Yakk - Adam Nevraumont
  Mar 21 at 18:15
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Yeah, just to be clear, it wasn't a criticism of your answer so much as a response to your discussion with πάντα in the comments. In this very limited case, where you're comparing to a string literal, it would obviously be fine to use wcscmp. I just wanted to explain why it's not a valid approach in general.
  
  – Cody Gray♦
  Mar 21 at 20:38
  
  

  
  
  
  

 | 
show 1 more comment

A lot here is wrong.

== on BSTR compares pointer values. Two L"Yes" being pointer-equal is implementation defined.

bool_expr?true:false is a noop.

bool val = wcscmp(pVal, L"Yes") == 0;

is probably what you want.

BSTR pVal = L"Yes";

is bad news; that isn't how you are supposed to create a BSTR. BSTR are supposed to be pascal-esque strings allocated in a specific region of memory.

BSTR pVal = SysAllocString(L"Yes");

is usually better.

Using wcscmp is valid on a BSTR, as BSTR is guaranteed null terminated. But assigning a null terminated string to a BSTR is not a good plan; the code consuming the BSTR may expect the length field to come before the first character.

It may even be a good plan to use _bstr_t which is a C++ wrapper around BSTR.

It is also usually a good idea to compare BSTR to BSTR and not using C APIs; a BSTR can contain embedded NULs, and C APIs stop at the first NUL.

_bstr_t pVal = L"Yes";

bool val = pVal == _bstr_t(L"Yes");

_bstr_t has an operator== that does a reasonable thing.

share|improve this answer

edited Mar 21 at 18:17

answered Mar 21 at 17:58

Yakk - Adam NevraumontYakk - Adam Nevraumont

188k21199384

bool val = wcscmp(pVal, L"Yes") == 0;

BSTR pVal = L"Yes";

BSTR pVal = SysAllocString(L"Yes");

_bstr_t pVal = L"Yes";

bool val = pVal == _bstr_t(L"Yes");

share|improve this answer

edited Mar 21 at 18:17

answered Mar 21 at 17:58

Yakk - Adam NevraumontYakk - Adam Nevraumont

188k21199384

answered Mar 21 at 17:58

Yakk - Adam NevraumontYakk - Adam Nevraumont

188k21199384

answered Mar 21 at 17:58

Yakk - Adam NevraumontYakk - Adam Nevraumont

188k21199384