What's the difference between (size_t)-1 and ~0?





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6















I've seen both (size_t)-1 and ~0 used to represent large numbers, or numbers with all their bits flipped.



Is there any difference between the two? If so, what is it?



I found this question: What is the difference between -1 and ~0, however it did not answer my question because I'm dealing with unsigned integers (such as size_t), as opposed to signed integers (such as int).






c unsigned ones-complement







share|improve this question























  • Note that ~0 is a signed quantity — you'd need ~0U to make it unsigned.

    – Jonathan Leffler
    3 hours ago











  • Should I edit that?

    – JL2210
    3 hours ago






  • 3





    Since you've got some answers which addresses ~0 rather than ~0U, best to leave it unchanged, I think, but note for the future that it is a good idea to be careful. You can change a question up until making the change would invalidate answers.

    – Jonathan Leffler
    3 hours ago




















6















I've seen both (size_t)-1 and ~0 used to represent large numbers, or numbers with all their bits flipped.



Is there any difference between the two? If so, what is it?



I found this question: What is the difference between -1 and ~0, however it did not answer my question because I'm dealing with unsigned integers (such as size_t), as opposed to signed integers (such as int).






c unsigned ones-complement







share|improve this question























  • Note that ~0 is a signed quantity — you'd need ~0U to make it unsigned.

    – Jonathan Leffler
    3 hours ago











  • Should I edit that?

    – JL2210
    3 hours ago






  • 3





    Since you've got some answers which addresses ~0 rather than ~0U, best to leave it unchanged, I think, but note for the future that it is a good idea to be careful. You can change a question up until making the change would invalidate answers.

    – Jonathan Leffler
    3 hours ago
















6












6








6








I've seen both (size_t)-1 and ~0 used to represent large numbers, or numbers with all their bits flipped.



Is there any difference between the two? If so, what is it?



I found this question: What is the difference between -1 and ~0, however it did not answer my question because I'm dealing with unsigned integers (such as size_t), as opposed to signed integers (such as int).






c unsigned ones-complement







share|improve this question














I've seen both (size_t)-1 and ~0 used to represent large numbers, or numbers with all their bits flipped.



Is there any difference between the two? If so, what is it?



I found this question: What is the difference between -1 and ~0, however it did not answer my question because I'm dealing with unsigned integers (such as size_t), as opposed to signed integers (such as int).






c unsigned ones-complement




c unsigned ones-complement






share|improve this question













share|improve this question











share|improve this question




share|improve this question










asked 3 hours ago









JL2210JL2210

622121




622121













  • Note that ~0 is a signed quantity — you'd need ~0U to make it unsigned.

    – Jonathan Leffler
    3 hours ago











  • Should I edit that?

    – JL2210
    3 hours ago






  • 3





    Since you've got some answers which addresses ~0 rather than ~0U, best to leave it unchanged, I think, but note for the future that it is a good idea to be careful. You can change a question up until making the change would invalidate answers.

    – Jonathan Leffler
    3 hours ago





















  • Note that ~0 is a signed quantity — you'd need ~0U to make it unsigned.

    – Jonathan Leffler
    3 hours ago











  • Should I edit that?

    – JL2210
    3 hours ago






  • 3





    Since you've got some answers which addresses ~0 rather than ~0U, best to leave it unchanged, I think, but note for the future that it is a good idea to be careful. You can change a question up until making the change would invalidate answers.

    – Jonathan Leffler
    3 hours ago



















Note that ~0 is a signed quantity — you'd need ~0U to make it unsigned.

– Jonathan Leffler
3 hours ago





Note that ~0 is a signed quantity — you'd need ~0U to make it unsigned.

– Jonathan Leffler
3 hours ago













Should I edit that?

– JL2210
3 hours ago





Should I edit that?

– JL2210
3 hours ago




3




3





Since you've got some answers which addresses ~0 rather than ~0U, best to leave it unchanged, I think, but note for the future that it is a good idea to be careful. You can change a question up until making the change would invalidate answers.

– Jonathan Leffler
3 hours ago







Since you've got some answers which addresses ~0 rather than ~0U, best to leave it unchanged, I think, but note for the future that it is a good idea to be careful. You can change a question up until making the change would invalidate answers.

– Jonathan Leffler
3 hours ago














3 Answers
3






active

oldest

votes


















5















What's the difference between (size_t)-1 and ~0?




Type and value differ.



(size_t)-1 is the same value as SIZE_MAX and has a type of size_t.



~0 is often -1 and has the type of int.




Assigning both of those to a size_t will result in SIZE_MAX.



size_t a = (size_t)-1; 

size_t b = ~0;


In the 2nd case, -1 is assigned to a b and undergoes a conversion first, wrapping around the -1 to the maximum size_t value.






share|improve this answer


























  • Comments are not for extended discussion; this conversation has been moved to chat.

    – Bhargav Rao♦
    2 hours ago



















4














(size_t)-1 is of type size_t. It typically has a value of 232-1 or 264-1 (4294967295 or 18446744073709551615).



~0 is of type int, and has the value -1 on a 2's-complement system (i.e., just about everywhere).



Both are likely to have the same bit pattern -- if int and size_t are the same size, which they very commonly are not.



If you want the maximum value of type size_t, you can use the SIZE_MAX macro, defined in <stdint.h>. If you're using an older implementation (pre-C99) that doesn't provide SIZE_MAX, (size_t)-1 will work. I'm not sure why you'd want to write ~0 rather than -1 -- unless perhaps you're considering non-two's-complement systems.






share|improve this answer


























  • Thanks for letting me know. I'll remember to define SIZE_MAX in my stdint.h implementation.

    – JL2210
    3 hours ago











  • Re; ~0 versus -1 - some compilers warn on implicit wrapping in constant expressions.

    – TLW
    23 mins ago



















0














Note that the previous answers assume a 2s complement machine (very likely to be the case these days, but not guaranteed).



If you had a sign-magnitude machine then -1 would have a sign bit and least significant bit set with all others clear, if you had a 1s complement machine then -1 would have all bits but the LSB set.



In all of these cases (including the common 2s complement machine) ~0 has all bits set.





share
























  • Note that in the question I'm asking about unsigned integers, so there's no such thing as a "sign bit".

    – JL2210
    1 hour ago








  • 2





    @JL2210 - note that the intermediate values of both ~0 and -1 are signed, not unsigned.

    – TLW
    25 mins ago











  • Ah. I understand now. I'll upvote as soon as this is edited.

    – JL2210
    4 mins ago












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3 Answers
3






active

oldest

votes








3 Answers
3






active

oldest

votes









active

oldest

votes






active

oldest

votes









5















What's the difference between (size_t)-1 and ~0?




Type and value differ.



(size_t)-1 is the same value as SIZE_MAX and has a type of size_t.



~0 is often -1 and has the type of int.




Assigning both of those to a size_t will result in SIZE_MAX.



size_t a = (size_t)-1; 

size_t b = ~0;


In the 2nd case, -1 is assigned to a b and undergoes a conversion first, wrapping around the -1 to the maximum size_t value.






share|improve this answer


























  • Comments are not for extended discussion; this conversation has been moved to chat.

    – Bhargav Rao♦
    2 hours ago
















5















What's the difference between (size_t)-1 and ~0?




Type and value differ.



(size_t)-1 is the same value as SIZE_MAX and has a type of size_t.



~0 is often -1 and has the type of int.




Assigning both of those to a size_t will result in SIZE_MAX.



size_t a = (size_t)-1; 

size_t b = ~0;


In the 2nd case, -1 is assigned to a b and undergoes a conversion first, wrapping around the -1 to the maximum size_t value.






share|improve this answer


























  • Comments are not for extended discussion; this conversation has been moved to chat.

    – Bhargav Rao♦
    2 hours ago














5












5








5








What's the difference between (size_t)-1 and ~0?




Type and value differ.



(size_t)-1 is the same value as SIZE_MAX and has a type of size_t.



~0 is often -1 and has the type of int.




Assigning both of those to a size_t will result in SIZE_MAX.



size_t a = (size_t)-1; 

size_t b = ~0;


In the 2nd case, -1 is assigned to a b and undergoes a conversion first, wrapping around the -1 to the maximum size_t value.






share|improve this answer
















What's the difference between (size_t)-1 and ~0?




Type and value differ.



(size_t)-1 is the same value as SIZE_MAX and has a type of size_t.



~0 is often -1 and has the type of int.




Assigning both of those to a size_t will result in SIZE_MAX.



size_t a = (size_t)-1; 

size_t b = ~0;


In the 2nd case, -1 is assigned to a b and undergoes a conversion first, wrapping around the -1 to the maximum size_t value.







share|improve this answer














share|improve this answer



share|improve this answer








edited 2 hours ago

























answered 3 hours ago









chuxchux

85.3k874157




85.3k874157













  • Comments are not for extended discussion; this conversation has been moved to chat.

    – Bhargav Rao♦
    2 hours ago



















  • Comments are not for extended discussion; this conversation has been moved to chat.

    – Bhargav Rao♦
    2 hours ago

















Comments are not for extended discussion; this conversation has been moved to chat.

– Bhargav Rao♦
2 hours ago





Comments are not for extended discussion; this conversation has been moved to chat.

– Bhargav Rao♦
2 hours ago













4














(size_t)-1 is of type size_t. It typically has a value of 232-1 or 264-1 (4294967295 or 18446744073709551615).



~0 is of type int, and has the value -1 on a 2's-complement system (i.e., just about everywhere).



Both are likely to have the same bit pattern -- if int and size_t are the same size, which they very commonly are not.



If you want the maximum value of type size_t, you can use the SIZE_MAX macro, defined in <stdint.h>. If you're using an older implementation (pre-C99) that doesn't provide SIZE_MAX, (size_t)-1 will work. I'm not sure why you'd want to write ~0 rather than -1 -- unless perhaps you're considering non-two's-complement systems.






share|improve this answer


























  • Thanks for letting me know. I'll remember to define SIZE_MAX in my stdint.h implementation.

    – JL2210
    3 hours ago











  • Re; ~0 versus -1 - some compilers warn on implicit wrapping in constant expressions.

    – TLW
    23 mins ago
















4














(size_t)-1 is of type size_t. It typically has a value of 232-1 or 264-1 (4294967295 or 18446744073709551615).



~0 is of type int, and has the value -1 on a 2's-complement system (i.e., just about everywhere).



Both are likely to have the same bit pattern -- if int and size_t are the same size, which they very commonly are not.



If you want the maximum value of type size_t, you can use the SIZE_MAX macro, defined in <stdint.h>. If you're using an older implementation (pre-C99) that doesn't provide SIZE_MAX, (size_t)-1 will work. I'm not sure why you'd want to write ~0 rather than -1 -- unless perhaps you're considering non-two's-complement systems.






share|improve this answer


























  • Thanks for letting me know. I'll remember to define SIZE_MAX in my stdint.h implementation.

    – JL2210
    3 hours ago











  • Re; ~0 versus -1 - some compilers warn on implicit wrapping in constant expressions.

    – TLW
    23 mins ago














4












4








4







(size_t)-1 is of type size_t. It typically has a value of 232-1 or 264-1 (4294967295 or 18446744073709551615).



~0 is of type int, and has the value -1 on a 2's-complement system (i.e., just about everywhere).



Both are likely to have the same bit pattern -- if int and size_t are the same size, which they very commonly are not.



If you want the maximum value of type size_t, you can use the SIZE_MAX macro, defined in <stdint.h>. If you're using an older implementation (pre-C99) that doesn't provide SIZE_MAX, (size_t)-1 will work. I'm not sure why you'd want to write ~0 rather than -1 -- unless perhaps you're considering non-two's-complement systems.






share|improve this answer















(size_t)-1 is of type size_t. It typically has a value of 232-1 or 264-1 (4294967295 or 18446744073709551615).



~0 is of type int, and has the value -1 on a 2's-complement system (i.e., just about everywhere).



Both are likely to have the same bit pattern -- if int and size_t are the same size, which they very commonly are not.



If you want the maximum value of type size_t, you can use the SIZE_MAX macro, defined in <stdint.h>. If you're using an older implementation (pre-C99) that doesn't provide SIZE_MAX, (size_t)-1 will work. I'm not sure why you'd want to write ~0 rather than -1 -- unless perhaps you're considering non-two's-complement systems.







share|improve this answer














share|improve this answer



share|improve this answer








edited 3 hours ago









Jonathan Leffler

575k956881041




575k956881041










answered 3 hours ago









Keith ThompsonKeith Thompson

195k26290484




195k26290484













  • Thanks for letting me know. I'll remember to define SIZE_MAX in my stdint.h implementation.

    – JL2210
    3 hours ago











  • Re; ~0 versus -1 - some compilers warn on implicit wrapping in constant expressions.

    – TLW
    23 mins ago



















  • Thanks for letting me know. I'll remember to define SIZE_MAX in my stdint.h implementation.

    – JL2210
    3 hours ago











  • Re; ~0 versus -1 - some compilers warn on implicit wrapping in constant expressions.

    – TLW
    23 mins ago

















Thanks for letting me know. I'll remember to define SIZE_MAX in my stdint.h implementation.

– JL2210
3 hours ago





Thanks for letting me know. I'll remember to define SIZE_MAX in my stdint.h implementation.

– JL2210
3 hours ago













Re; ~0 versus -1 - some compilers warn on implicit wrapping in constant expressions.

– TLW
23 mins ago





Re; ~0 versus -1 - some compilers warn on implicit wrapping in constant expressions.

– TLW
23 mins ago











0














Note that the previous answers assume a 2s complement machine (very likely to be the case these days, but not guaranteed).



If you had a sign-magnitude machine then -1 would have a sign bit and least significant bit set with all others clear, if you had a 1s complement machine then -1 would have all bits but the LSB set.



In all of these cases (including the common 2s complement machine) ~0 has all bits set.





share
























  • Note that in the question I'm asking about unsigned integers, so there's no such thing as a "sign bit".

    – JL2210
    1 hour ago








  • 2





    @JL2210 - note that the intermediate values of both ~0 and -1 are signed, not unsigned.

    – TLW
    25 mins ago











  • Ah. I understand now. I'll upvote as soon as this is edited.

    – JL2210
    4 mins ago
















0














Note that the previous answers assume a 2s complement machine (very likely to be the case these days, but not guaranteed).



If you had a sign-magnitude machine then -1 would have a sign bit and least significant bit set with all others clear, if you had a 1s complement machine then -1 would have all bits but the LSB set.



In all of these cases (including the common 2s complement machine) ~0 has all bits set.





share
























  • Note that in the question I'm asking about unsigned integers, so there's no such thing as a "sign bit".

    – JL2210
    1 hour ago








  • 2





    @JL2210 - note that the intermediate values of both ~0 and -1 are signed, not unsigned.

    – TLW
    25 mins ago











  • Ah. I understand now. I'll upvote as soon as this is edited.

    – JL2210
    4 mins ago














0












0








0







Note that the previous answers assume a 2s complement machine (very likely to be the case these days, but not guaranteed).



If you had a sign-magnitude machine then -1 would have a sign bit and least significant bit set with all others clear, if you had a 1s complement machine then -1 would have all bits but the LSB set.



In all of these cases (including the common 2s complement machine) ~0 has all bits set.





share













Note that the previous answers assume a 2s complement machine (very likely to be the case these days, but not guaranteed).



If you had a sign-magnitude machine then -1 would have a sign bit and least significant bit set with all others clear, if you had a 1s complement machine then -1 would have all bits but the LSB set.



In all of these cases (including the common 2s complement machine) ~0 has all bits set.






share











share


share










answered 1 hour ago









SoronelHaetirSoronelHaetir

7,1711514




7,1711514













  • Note that in the question I'm asking about unsigned integers, so there's no such thing as a "sign bit".

    – JL2210
    1 hour ago








  • 2





    @JL2210 - note that the intermediate values of both ~0 and -1 are signed, not unsigned.

    – TLW
    25 mins ago











  • Ah. I understand now. I'll upvote as soon as this is edited.

    – JL2210
    4 mins ago



















  • Note that in the question I'm asking about unsigned integers, so there's no such thing as a "sign bit".

    – JL2210
    1 hour ago








  • 2





    @JL2210 - note that the intermediate values of both ~0 and -1 are signed, not unsigned.

    – TLW
    25 mins ago











  • Ah. I understand now. I'll upvote as soon as this is edited.

    – JL2210
    4 mins ago

















Note that in the question I'm asking about unsigned integers, so there's no such thing as a "sign bit".

– JL2210
1 hour ago







Note that in the question I'm asking about unsigned integers, so there's no such thing as a "sign bit".

– JL2210
1 hour ago






2




2





@JL2210 - note that the intermediate values of both ~0 and -1 are signed, not unsigned.

– TLW
25 mins ago





@JL2210 - note that the intermediate values of both ~0 and -1 are signed, not unsigned.

– TLW
25 mins ago













Ah. I understand now. I'll upvote as soon as this is edited.

– JL2210
4 mins ago





Ah. I understand now. I'll upvote as soon as this is edited.

– JL2210
4 mins ago


















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