[英]memset() in C not initialising to a const double;
Hi I have the following code written in C for x86, 嗨,我有以下用C语言为x86编写的代码,
const double N = 4;
const double C = 1.0 / N; <---- 0.2500
double *array = (double*)calloc(10, sizeof(double));
memset(array, C, 10);
the result of the memset only returns 0.0000 for each element instead of the value stored in C.. memset的结果只为每个元素返回0.0000,而不是存储在C中的值。
can anyone please help? 谁能帮忙吗?
memset
initializes a block of memory with a given byte value. memset
用给定的字节值初始化一个内存块。 Bytes are unsigned char
, a much smaller unit than double
which uses 8 bytes on your architecture. 字节是unsigned char
,比在体系结构中使用8个字节的double
单位小得多。 Unless all the bytes of the double
value C
are identical, memset
cannot be used to initialize an array of double
values. 除非double
memset
值C
所有字节都相同,否则无法使用memset
初始化double
值数组。 On IEEE-754 compliant systems such as the various x86 variants, +0.0
has all bytes with all bits 0
, so you could use memset(array[i], 0, 10 * sizeof(double))
to initialize the array to 0.0
, but this is neither readable nor portable. 在符合IEEE-754的系统(例如各种x86变体)上,+ +0.0
所有字节的位均为0
,因此您可以使用memset(array[i], 0, 10 * sizeof(double))
将数组初始化为0.0
,但这既不可读也不便携。 For most other values, It not possible at all. 对于大多数其他值,根本不可能。
You must use a simple for
loop: 您必须使用一个简单的for
循环:
for (int i = 0; i < 10; i++)
array[i] = C;
The loop will be optimized by the compiler, especially if C is a compile time constant. 该循环将由编译器优化,特别是如果C是编译时间常数。
void *memset(void *s, int c, size_t n);
memset accepts an int or a constant byte to fill the memory. memset接受一个int或一个常量字节来填充内存。
The value provide by you is a double
. 您提供的值是double
。 So how memset
is going to deal with it ? 那么memset
将如何处理呢?
The value provided by you will be implicitly casted to int and then the casted value will again be casted to unsigned char to get a byte value . 您提供的值将隐式转换为int,然后将转换值再次转换为unsigned char以获取字节值 。
Also, the size_t argument of memset is the number of bytes. 同样,memset的size_t参数是字节数。 You should use, 10 * sizeof(double)
instead of just 10
. 您应该使用10 * sizeof(double)
而不是10
。
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