C++: Built-in arrays
-2
I thought that built-in arrays in C++ are statically allocated. But the following code works:
//...
int x;
std::cin >> x;
const int cx = x;
int array[cx];
//...
Why does it?
c++
edited Nov 20 '18 at 19:49
Fei Xiang
2,1064822
asked Nov 20 '18 at 19:17
GlechGlech
6
add a comment |
-2
I thought that built-in arrays in C++ are statically allocated. But the following code works:
//...
int x;
std::cin >> x;
const int cx = x;
int array[cx];
//...
Why does it?
c++
edited Nov 20 '18 at 19:49
Fei Xiang
2,1064822
asked Nov 20 '18 at 19:17
GlechGlech
6
8
That code works on some compilers that offer default-on extensions for variable length array. It doesn't work on other compilers and is not portable c++. You're being tricked by your compiler into thinking your code is valid c++. Another example of why you can't learn c++ by trial and error.
– François Andrieux
Nov 20 '18 at 19:18
One reason Variable Length Arrays are bad:xcan support numbers that are very big. Bigger than the amount of Automatic storage available to that array. Now multiply that large number by the size of anint. Using an array of that size will commonly manifest as a stack overflow and much debugging can ensue as a result.
– user4581301
Nov 20 '18 at 19:58
add a comment |
-2
-2
-2
I thought that built-in arrays in C++ are statically allocated. But the following code works:
//...
int x;
std::cin >> x;
const int cx = x;
int array[cx];
//...
Why does it?
c++
edited Nov 20 '18 at 19:49
Fei Xiang
2,1064822
asked Nov 20 '18 at 19:17
GlechGlech
6
I thought that built-in arrays in C++ are statically allocated. But the following code works:
//...
int x;
std::cin >> x;
const int cx = x;
int array[cx];
//...
Why does it?
c++
c++
edited Nov 20 '18 at 19:49
Fei Xiang
2,1064822
asked Nov 20 '18 at 19:17
GlechGlech
6
edited Nov 20 '18 at 19:49
Fei Xiang
2,1064822
asked Nov 20 '18 at 19:17
GlechGlech
6
edited Nov 20 '18 at 19:49
Fei Xiang
2,1064822
edited Nov 20 '18 at 19:49
Fei Xiang
2,1064822
edited Nov 20 '18 at 19:49
Fei Xiang
2,1064822
2,1064822
asked Nov 20 '18 at 19:17
GlechGlech
6
asked Nov 20 '18 at 19:17
GlechGlech
6
asked Nov 20 '18 at 19:17
GlechGlech
6
6
8
That code works on some compilers that offer default-on extensions for variable length array. It doesn't work on other compilers and is not portable c++. You're being tricked by your compiler into thinking your code is valid c++. Another example of why you can't learn c++ by trial and error.
– François Andrieux
Nov 20 '18 at 19:18
One reason Variable Length Arrays are bad:xcan support numbers that are very big. Bigger than the amount of Automatic storage available to that array. Now multiply that large number by the size of anint. Using an array of that size will commonly manifest as a stack overflow and much debugging can ensue as a result.
– user4581301
Nov 20 '18 at 19:58
add a comment |
8
That code works on some compilers that offer default-on extensions for variable length array. It doesn't work on other compilers and is not portable c++. You're being tricked by your compiler into thinking your code is valid c++. Another example of why you can't learn c++ by trial and error.
– François Andrieux
Nov 20 '18 at 19:18
One reason Variable Length Arrays are bad:xcan support numbers that are very big. Bigger than the amount of Automatic storage available to that array. Now multiply that large number by the size of anint. Using an array of that size will commonly manifest as a stack overflow and much debugging can ensue as a result.
– user4581301
Nov 20 '18 at 19:58
8
8
That code works on some compilers that offer default-on extensions for variable length array. It doesn't work on other compilers and is not portable c++. You're being tricked by your compiler into thinking your code is valid c++. Another example of why you can't learn c++ by trial and error.
– François Andrieux
Nov 20 '18 at 19:18
That code works on some compilers that offer default-on extensions for variable length array. It doesn't work on other compilers and is not portable c++. You're being tricked by your compiler into thinking your code is valid c++. Another example of why you can't learn c++ by trial and error.
– François Andrieux
Nov 20 '18 at 19:18
One reason Variable Length Arrays are bad:
x can support numbers that are very big. Bigger than the amount of Automatic storage available to that array. Now multiply that large number by the size of an int. Using an array of that size will commonly manifest as a stack overflow and much debugging can ensue as a result.– user4581301
Nov 20 '18 at 19:58
One reason Variable Length Arrays are bad:
x can support numbers that are very big. Bigger than the amount of Automatic storage available to that array. Now multiply that large number by the size of an int. Using an array of that size will commonly manifest as a stack overflow and much debugging can ensue as a result.– user4581301
Nov 20 '18 at 19:58
add a comment |
1 Answer
1
active
oldest
votes
3
Variable length arrays are not part of the C++ standard, however your compiler allows it. If you use the -pedantic-errors option with your compiler (assuming g++), this will throw an error as that option strictly enforces the standard.
answered Nov 20 '18 at 19:40
jdrdjdrd
1297
1
-pedanticcauses the compiler to emit warnings, not errors. You need to add on-Werroror-pedantic-errorsto get an compilation-halting error. That said,-Werroris something I recommend to anyone learning C++. Warnings are the first line of defense against logic errors and you should not ignore them.
– user4581301
Nov 20 '18 at 19:47
thanks, edited my answer to reflect that
– jdrd
Nov 20 '18 at 19:51
add a comment |
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1 Answer
1
active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
3
Variable length arrays are not part of the C++ standard, however your compiler allows it. If you use the -pedantic-errors option with your compiler (assuming g++), this will throw an error as that option strictly enforces the standard.
answered Nov 20 '18 at 19:40
jdrdjdrd
1297
1
-pedanticcauses the compiler to emit warnings, not errors. You need to add on-Werroror-pedantic-errorsto get an compilation-halting error. That said,-Werroris something I recommend to anyone learning C++. Warnings are the first line of defense against logic errors and you should not ignore them.
– user4581301
Nov 20 '18 at 19:47
thanks, edited my answer to reflect that
– jdrd
Nov 20 '18 at 19:51
add a comment |
3
Variable length arrays are not part of the C++ standard, however your compiler allows it. If you use the -pedantic-errors option with your compiler (assuming g++), this will throw an error as that option strictly enforces the standard.
answered Nov 20 '18 at 19:40
jdrdjdrd
1297
1
-pedanticcauses the compiler to emit warnings, not errors. You need to add on-Werroror-pedantic-errorsto get an compilation-halting error. That said,-Werroris something I recommend to anyone learning C++. Warnings are the first line of defense against logic errors and you should not ignore them.
– user4581301
Nov 20 '18 at 19:47
thanks, edited my answer to reflect that
– jdrd
Nov 20 '18 at 19:51
add a comment |
3
3
3
Variable length arrays are not part of the C++ standard, however your compiler allows it. If you use the -pedantic-errors option with your compiler (assuming g++), this will throw an error as that option strictly enforces the standard.
answered Nov 20 '18 at 19:40
jdrdjdrd
1297
Variable length arrays are not part of the C++ standard, however your compiler allows it. If you use the -pedantic-errors option with your compiler (assuming g++), this will throw an error as that option strictly enforces the standard.
answered Nov 20 '18 at 19:40
jdrdjdrd
1297
edited Nov 20 '18 at 19:50
answered Nov 20 '18 at 19:40
jdrdjdrd
1297
answered Nov 20 '18 at 19:40
jdrdjdrd
1297
answered Nov 20 '18 at 19:40
jdrdjdrd
1297
1297
1
-pedanticcauses the compiler to emit warnings, not errors. You need to add on-Werroror-pedantic-errorsto get an compilation-halting error. That said,-Werroris something I recommend to anyone learning C++. Warnings are the first line of defense against logic errors and you should not ignore them.
– user4581301
Nov 20 '18 at 19:47
thanks, edited my answer to reflect that
– jdrd
Nov 20 '18 at 19:51
add a comment |
1
-pedanticcauses the compiler to emit warnings, not errors. You need to add on-Werroror-pedantic-errorsto get an compilation-halting error. That said,-Werroris something I recommend to anyone learning C++. Warnings are the first line of defense against logic errors and you should not ignore them.
– user4581301
Nov 20 '18 at 19:47
thanks, edited my answer to reflect that
– jdrd
Nov 20 '18 at 19:51
1
1
-pedantic causes the compiler to emit warnings, not errors. You need to add on -Werror or -pedantic-errors to get an compilation-halting error. That said, -Werror is something I recommend to anyone learning C++. Warnings are the first line of defense against logic errors and you should not ignore them.– user4581301
Nov 20 '18 at 19:47
-pedantic causes the compiler to emit warnings, not errors. You need to add on -Werror or -pedantic-errors to get an compilation-halting error. That said, -Werror is something I recommend to anyone learning C++. Warnings are the first line of defense against logic errors and you should not ignore them.– user4581301
Nov 20 '18 at 19:47
thanks, edited my answer to reflect that
– jdrd
Nov 20 '18 at 19:51
thanks, edited my answer to reflect that
– jdrd
Nov 20 '18 at 19:51
add a comment |
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8
That code works on some compilers that offer default-on extensions for variable length array. It doesn't work on other compilers and is not portable c++. You're being tricked by your compiler into thinking your code is valid c++. Another example of why you can't learn c++ by trial and error.
– François Andrieux
Nov 20 '18 at 19:18
One reason Variable Length Arrays are bad:
xcan support numbers that are very big. Bigger than the amount of Automatic storage available to that array. Now multiply that large number by the size of anint. Using an array of that size will commonly manifest as a stack overflow and much debugging can ensue as a result.– user4581301
Nov 20 '18 at 19:58