memcmp

Test of 8 subsequent bytes isn't translated into a single compare instruction

由 我与影子孤独终老i 提交于 2020-08-27 22:14:09
问题 Motivated by this question, I compared three different functions for checking if 8 bytes pointed to by the argument are zeros (note that in the original question, characters are compared with '0' , not 0 ): bool f1(const char *ptr) { for (int i = 0; i < 8; i++) if (ptr[i]) return false; return true; } bool f2(const char *ptr) { bool res = true; for (int i = 0; i < 8; i++) res &= (ptr[i] == 0); return res; } bool f3(const char *ptr) { static const char tmp[8]{}; return !std::memcmp(ptr, tmp, 8

Test of 8 subsequent bytes isn't translated into a single compare instruction

由 白昼怎懂夜的黑 提交于 2020-08-27 22:12:57
问题 Motivated by this question, I compared three different functions for checking if 8 bytes pointed to by the argument are zeros (note that in the original question, characters are compared with '0' , not 0 ): bool f1(const char *ptr) { for (int i = 0; i < 8; i++) if (ptr[i]) return false; return true; } bool f2(const char *ptr) { bool res = true; for (int i = 0; i < 8; i++) res &= (ptr[i] == 0); return res; } bool f3(const char *ptr) { static const char tmp[8]{}; return !std::memcmp(ptr, tmp, 8

Test of 8 subsequent bytes isn't translated into a single compare instruction

由 喜你入骨 提交于 2020-08-27 22:12:26
问题 Motivated by this question, I compared three different functions for checking if 8 bytes pointed to by the argument are zeros (note that in the original question, characters are compared with '0' , not 0 ): bool f1(const char *ptr) { for (int i = 0; i < 8; i++) if (ptr[i]) return false; return true; } bool f2(const char *ptr) { bool res = true; for (int i = 0; i < 8; i++) res &= (ptr[i] == 0); return res; } bool f3(const char *ptr) { static const char tmp[8]{}; return !std::memcmp(ptr, tmp, 8

Test of 8 subsequent bytes isn't translated into a single compare instruction

由 久未见 提交于 2020-08-27 22:12:07
问题 Motivated by this question, I compared three different functions for checking if 8 bytes pointed to by the argument are zeros (note that in the original question, characters are compared with '0' , not 0 ): bool f1(const char *ptr) { for (int i = 0; i < 8; i++) if (ptr[i]) return false; return true; } bool f2(const char *ptr) { bool res = true; for (int i = 0; i < 8; i++) res &= (ptr[i] == 0); return res; } bool f3(const char *ptr) { static const char tmp[8]{}; return !std::memcmp(ptr, tmp, 8

memcmp linker error Visual Studio 2015

由 Deadly 提交于 2020-01-11 10:45:48
问题 I have a visual studio 2012 c++ project. I recently uninstalled it and installed visual studio 2015 and upgraded the project. When i am building the project, getting error as shown below: Error LNK2019 unresolved external symbol _memcmp referenced in function Moreover i have not used anywhere in my code memcmp fucntion. I used the linker verbose function and could see below in output file: Found _memcmp Referenced in MyC++Project.obj Referenced in libcpmtd.lib(xstrcoll.obj) Loaded

memcmp but need to compare block with fixed value

由 蓝咒 提交于 2019-12-23 09:11:03
问题 I need to compare a block of memory to a fixed value in C. Can I do this with memcmp? Something like: memcmp (starting_address , fixed_value , num_byte) I need fixed_value to be a fixed value not the starting address of a block. Writing the fixed value to an entire temporary memory block is not an option because I have limited space. Using a loop to write and check memory one by one is not an option because it's very slow. If it's not possible can anyone tell me a solution that is as fast (or

C array comparison

由 为君一笑 提交于 2019-12-22 06:44:13
问题 Is the defacto method for comparing arrays (in C) to use memcmp from string.h ? I want to compare arrays of ints and doubles in my unit tests I am unsure whether to use something like: double a[] = {1.0, 2.0, 3.0}; double b[] = {1.0, 2.0, 3.0}; size_t n = 3; if (! memcmp(a, b, n * sizeof(double))) /* arrays equal */ or to write a bespoke is_array_equal(a, b, n) type function? 回答1: memcmp would do an exact comparison, which is seldom a good idea for floats, and would not follow the rule that

Using file i/o to read byte length

由 丶灬走出姿态 提交于 2019-12-11 10:21:27
问题 I'm trying to find the byte length of two different files with the following code, but get the byte length as 1, which is obviously wrong. In the long run, I'm trying to compare memory positions of each file and print out where they differ as you'll see. So I wasn't getting anywhere, and did printf statements to see where the problem could be. Therefore, it looks as if my length isn't properly calculating. Side note that may help with my issue - I found this for memcmp, but does this mean I

memcmp，memicmp函数

由 你说的曾经没有我的故事 提交于 2019-12-08 17:22:45
函数原型：extern int memcmp(void *str1, void *str2, unsigned int n) 参数说明：str1和str2为指定作比较的字符串，比较两个字符串的前n个字节。 所在库名：#include <string.h> 函数功能：比较字符串str1和str2在内存区域中的的前n个字节是否相同。 返回说明：当str1<str12时，返回值<0；当str11=str12时，返回值=0；当str11>str12时，返回值>0。 其它说明：暂时无。 实例： #include < string .h > #include < stdio.h > int main() ... { char * str1 = " I'm sky2098,welcome to my website! " ; char * str2 = " I'm sky2098,please do not call me sky2098! " ; int inttemp; inttemp = memcmp(str1,str2,strlen( " I'm sky2098, " )); // 比较str1和str2在内存区中前strlen("I'm sky2098,")个字节是否相等 if (inttemp == 0 ) ... { printf( " str1 and str2 has n

C语言memcmp()函数：比较内存前n个字节

由 蹲街弑〆低调 提交于 2019-12-08 17:22:31
头文件：#include <string.h> 定义函数：int memcmp (const void *s1, const void *s2, size_t n); 函数说明：memcmp()用来比较s1 和s2 所指的内存区间前n 个字符。 字符串大小的比较是以ASCII 码表上的顺序来决定，次顺序亦为字符的值。memcmp()首先将s1 第一个字符值减去s2 第一个字符的值，若差为0 则再继续比较下个字符，若差值不为0 则将差值返回。例如，字符串"Ac"和"ba"比较则会返回字符'A'(65)和'b'(98)的差值(－33)。 返回值：若参数s1 和s2 所指的内存内容都完全相同则返回0 值。s1 若大于s2 则返回大于0 的值。s1 若小于s2 则返回小于0 的值。 范例 #include <string.h> main () { char * a = "aBcDeF" ; char * b = "AbCdEf" ; char * c = "aacdef" ; char * d = "aBcDeF" ; printf ( "memcmp(a, b):%d \n " , memcmp (( void *) a , ( void *) b , 6 )); printf ( "memcmp(a, c):%d \n " , memcmp (( void *) a , ( void
订阅 memcmp