variable-length-array

Is there any overhead for using variable-length arrays?

由 跟風遠走 提交于 2019-11-26 12:13:19
问题 Is there some overhead of using variable-length arrays? Could the size of array be passed via command line argument at run time? Why is it introduced, compared to automatic and dynamically allocating an array? 回答1: VLA does have some overhead (compared to "ordinary" named compile-time-sized array). Firstly, it has run-time length and yet the language provides you with means to obtain the actual size of the array at run-time (using sizeof ). This immediately means that the actual size of the

Enabling VLAs (variable length arrays) in MS Visual C++?

由 戏子无情 提交于 2019-11-26 10:42:57
How can i enable the use of VLAs, variable length arrays as defined in C99, in MS Visual C++ or that is not possible at all? Yes i know that the C++ standard is based on C89 and that VLAs are not available in C89 standard and thus aren't available in C++, but MSVC++ is supposed to to be a C compiler also, a behavior that can be switched on using the /TC compiler parameter ( Compile as C Code (/TC) ). But doing so does not seem to enable VLAs and the compiling process fails with the same errors when building as C++( Compile as C++ Code (/TP) ). Maybe MSVC++ C compiler is C89 compliant only or i

Are variable length arrays there in c++?

由 一个人想着一个人 提交于 2019-11-26 08:54:21
问题 I had always thought that variable length arrays were not allowed in c++(Refer :Why aren't variable-length arrays part of the C++ standard?) .But than why does this code compile and work? #include <iostream> using namespace std; int main () { int n; cin >> n; int a[n]; for (int i=0; i<n; i++) { a[i] = i; } for (int i=0; i<n; i++) { cout << a[i] << endl; } } 回答1: The current C++ standard does not require that compilers VLAs. However, compiler vendors are permitted to support VLAs as an

Which compiler should I trust?

由 人走茶凉 提交于 2019-11-26 07:50:27
问题 This is going to be some what of a newbie question but I was trying to work on a small exercise in the C Language (not C++ ) and I was running into some issues. Say I wanted to use an array within a method whose size depended on one of the arguments: void someFunc(int arSize) { char charArray[arSize]; // DO STUFF ... } When I try to compile this as a .c file within Visual Studio 2013 I get an error saying that a non-constant array size is not allowed. However the same code works within

Is it safe to use variable-length arrays?

由 妖精的绣舞 提交于 2019-11-26 07:46:20
问题 I have a concern about variable-length arrays. When I want to allocate an array dynamically, I\'ll get null, if it is not possible to allocate enough memory and I can respond to this properly in my program. With a variable length array I don\'t get this information. What should I do with this? 回答1: You are right that VLA's are basically always unsafe. The only exception is if you ensure that you never make them larger than a size you would feel safe making a fixed-size array, and in that case

What&#39;s the difference between a VLA and dynamic memory allocation via malloc?

由 岁酱吖の 提交于 2019-11-26 05:39:10
问题 I was curious with this: What is the diference between: const int MAX_BUF = 1000; char* Buffer = malloc(MAX_BUF); and: char Buffer[MAX_BUF]; 回答1: Case 1: In char Buffer[MAX_BUF]; Buffer is an array of size MAX_BUF . The allocation technique is called VLA. Case 2: In const int MAX_BUF = 1000; char* Buffer = malloc(MAX_BUF); Buffer is a pointer which is allocated a memory of size MAX_BUF which is 1000 . and, an array is not the same as a pointer, and C-FAQ has a Very Good collection detailing

Convert Python sequence to NumPy array, filling missing values

由 血红的双手。 提交于 2019-11-26 05:06:16
The implicit conversion of a Python sequence of variable-length lists into a NumPy array cause the array to be of type object . v = [[1], [1, 2]] np.array(v) >>> array([[1], [1, 2]], dtype=object) Trying to force another type will cause an exception: np.array(v, dtype=np.int32) ValueError: setting an array element with a sequence. What is the most efficient way to get a dense NumPy array of type int32, by filling the "missing" values with a given placeholder? From my sample sequence v , I would like to get something like this, if 0 is the placeholder array([[1, 0], [1, 2]], dtype=int32) You

Difference between array type and array allocated with malloc

由 感情迁移 提交于 2019-11-26 03:41:52
Today I was helping a friend of mine with some C code, and I've found some strange behavior that I couldn't explain him why it was happening. We had TSV file with a list of integers, with an int each line. The first line was the number of lines the list had. We also had a c file with a very simple "readfile". The first line was read to n, the number of lines, then there was an initialization of: int list[n] and finally a for loop of n with a fscanf. For small n's (till ~100.000), everything was fine. However, we've found that when n was big (10^6), a segfault would occur. Finally, we changed

Enabling VLAs (variable length arrays) in MS Visual C++?

由 笑着哭i 提交于 2019-11-26 02:02:29
问题 How can I enable the use of VLAs, variable length arrays as defined in C99, in MS Visual C++ or that is not possible at all? Yes I know that the C++ standard is based on C89 and that VLAs are not available in C89 standard and thus aren\'t available in C++, but MSVC++ is supposed to be a C compiler also, a behavior that can be switched on using the /TC compiler parameter ( Compile as C Code (/TC) ). But doing so does not seem to enable VLAs and the compiling process fails with the same errors

Convert Python sequence to NumPy array, filling missing values

由 谁都会走 提交于 2019-11-26 01:40:43
问题 The implicit conversion of a Python sequence of variable-length lists into a NumPy array cause the array to be of type object . v = [[1], [1, 2]] np.array(v) >>> array([[1], [1, 2]], dtype=object) Trying to force another type will cause an exception: np.array(v, dtype=np.int32) ValueError: setting an array element with a sequence. What is the most efficient way to get a dense NumPy array of type int32, by filling the \"missing\" values with a given placeholder? From my sample sequence v , I
订阅 variable-length-array