c

问题 I've been trying to convert an array [R,G,B,..] in Mat object with opencv. But is returning wrong data, someone knows why? double data[12] = {0,0,255,0,0,255,0,0,255,0,0,255}; Mat src = Mat(2,2, CV_16UC3, data); and returns: M = [0, 0, 0, 0, 0, 0; 0, 0, 0, 0, 57344, 16495] EDIT: Solved! use uchar instead double, and CV_8UC3 回答1: i think, you wanted: uchar data[12] = {0,0,255,0,0,255,0,0,255,0,0,255}; Mat src = Mat(2,2, CV_8UC3, data); (all red, 2x2 rbg image) 来源： https://stackoverflow.com

问题 I'm trying to enhance the performance of my code by using the 256bit vector (Intel intrinsics - AVX). I have an I7 Gen.4 (Haswell architecture) processor supporting SSE1 to SSE4.2 and AVX/AVX2 Extensions. This is the code snippet that I'm trying to enhance: /* code snipet */ kfac1 = kfac + factor; /* 7 cycles for 7 additions */ kfac2 = kfac1 + factor; kfac3 = kfac2 + factor; kfac4 = kfac3 + factor; kfac5 = kfac4 + factor; kfac6 = kfac5 + factor; kfac7 = kfac6 + factor; k1fac1 = k1fac +

问题 I've been trying to convert an array [R,G,B,..] in Mat object with opencv. But is returning wrong data, someone knows why? double data[12] = {0,0,255,0,0,255,0,0,255,0,0,255}; Mat src = Mat(2,2, CV_16UC3, data); and returns: M = [0, 0, 0, 0, 0, 0; 0, 0, 0, 0, 57344, 16495] EDIT: Solved! use uchar instead double, and CV_8UC3 回答1: i think, you wanted: uchar data[12] = {0,0,255,0,0,255,0,0,255,0,0,255}; Mat src = Mat(2,2, CV_8UC3, data); (all red, 2x2 rbg image) 来源： https://stackoverflow.com

问题 I'm trying to enhance the performance of my code by using the 256bit vector (Intel intrinsics - AVX). I have an I7 Gen.4 (Haswell architecture) processor supporting SSE1 to SSE4.2 and AVX/AVX2 Extensions. This is the code snippet that I'm trying to enhance: /* code snipet */ kfac1 = kfac + factor; /* 7 cycles for 7 additions */ kfac2 = kfac1 + factor; kfac3 = kfac2 + factor; kfac4 = kfac3 + factor; kfac5 = kfac4 + factor; kfac6 = kfac5 + factor; kfac7 = kfac6 + factor; k1fac1 = k1fac +

问题 Is the behavior implementation defined? If NULL and size == 0 are passed to realloc() : int main(void) { int *ptr = NULL; ptr = realloc(ptr, 0); if(ptr == NULL) { printf("realloc fails.\n"); goto Exit; } printf("Happy Scenario.\n"); Exit: printf("Inside goto.\n"); return 0; } The above code should print "realloc fails", right? But it is not? I've read somewhere that this call to realloc may return NULL also. When does that happen? 回答1: This behavior is implementation defined. From the C

问题 #include <stdio.h> #include <string.h> #include <errno.h> #include <fcntl.h> int main() { int fd; if ((fd = open("/home/zhangke", O_DIRECTORY | O_RDWR)) ==-1) { printf("error %s\n", strerror(errno)); return -1; } return 0; } /home/zhangke is a directory and it exists . I get error Is a directory , so, how can I use open() to get a fd of a directory correctly? 回答1: Use O_RDONLY instead of O_RDWR as the access mode. From the open(2) error list: EISDIR pathname refers to a directory and the

问题 I've got 2 chars. Char 128 and Char 2 . How do I turn these chars into the Short 640 in C? I've tried unsigned short getShort(unsigned char* array, int offset) { short returnVal; char* a = slice(array, offset, offset+2); memcpy(&returnVal, a, 2); free(a); return returnVal; } But that didn't work, it just displays it as 128 . What's the preferred method? 回答1: I found that the accepted answer was nearly correct, except i'd run into a bug where sometimes the top byte of the result would be 0xff

问题 In C, using POSIX calls, how can I determine if a path is inside a target directory? For example, a web server has its root directory in /srv , this is getcwd() for the daemon. When parsing a request for /index.html , it returns the contents of /srv/index.html . How can I filter out requests for paths outside of /srv ? /../etc/passwd , /valid/../../etc/passwd , etc. Splitting the path at / and rejecting any array containing .. will break valid accesses /srv/valid/../index.html . Is there a

问题 How do functions such as printf extract digits from a floating point number? I understand how this could be done in principle. Given a number x , of which you want the first n digits, scale x by a power of 10 so that x is between pow(10, n) and pow(10, n-1) . Then convert x into an integer, and take the digits of the integer. I tried this, and it worked. Sort of. My answer was identical to the answer given by printf for the first 16 decimal digits, but tended to differ on the ones after that.

问题 How do functions such as printf extract digits from a floating point number? I understand how this could be done in principle. Given a number x , of which you want the first n digits, scale x by a power of 10 so that x is between pow(10, n) and pow(10, n-1) . Then convert x into an integer, and take the digits of the integer. I tried this, and it worked. Sort of. My answer was identical to the answer given by printf for the first 16 decimal digits, but tended to differ on the ones after that.