c

问题 6.4.3 Universal character names A universal character name shall not specify a character whose short identifier is less than 00A0 other than 0024 ($), 0040 (@), or 0060 (`), nor one in the range D800 through DFFF inclusive. Besides the fact that it is no longer "universal" with restrictions like this, I can't think of good reasons for such a restriction. Anyone knows the backstory? 回答1: D800 through DFFF inclusive are not valid code points; they are high and low surrogates, which can only be

问题 I'm implementing linked lists using structures. I have a structure - typedef struct llist node; typedef node *nodeptr; struct llist { int data; nodeptr next; }; Now lets say I declare a variable nodeptr *ptr; . How do I access the members data and next using ptr ? 回答1: You deference the first pointer and then the second one. To access the data and next in the structure statement would like this (*ptr)->data = 5; (*ptr)->next = temp; brackets around ptr is required since -> has higher priority

问题 In one of the books that I am reading, following function is used to determine 2's complement integer multiplication overflow. int tmult_ok(int x, int y) { int p = x*y; return !x || p/x == y; } While this works, how do I prove its correctness in all the cases? How do I ensure that p != x*y when there is an overflow? Here is what I understand: When you multiply 2 integers of size "w- bits", the result can be 2w bits. The computation truncates higher order w bits. So we are left with lower

问题 In one of the books that I am reading, following function is used to determine 2's complement integer multiplication overflow. int tmult_ok(int x, int y) { int p = x*y; return !x || p/x == y; } While this works, how do I prove its correctness in all the cases? How do I ensure that p != x*y when there is an overflow? Here is what I understand: When you multiply 2 integers of size "w- bits", the result can be 2w bits. The computation truncates higher order w bits. So we are left with lower

问题 In one of the books that I am reading, following function is used to determine 2's complement integer multiplication overflow. int tmult_ok(int x, int y) { int p = x*y; return !x || p/x == y; } While this works, how do I prove its correctness in all the cases? How do I ensure that p != x*y when there is an overflow? Here is what I understand: When you multiply 2 integers of size "w- bits", the result can be 2w bits. The computation truncates higher order w bits. So we are left with lower

问题 I'm implementing linked lists using structures. I have a structure - typedef struct llist node; typedef node *nodeptr; struct llist { int data; nodeptr next; }; Now lets say I declare a variable nodeptr *ptr; . How do I access the members data and next using ptr ? 回答1: You deference the first pointer and then the second one. To access the data and next in the structure statement would like this (*ptr)->data = 5; (*ptr)->next = temp; brackets around ptr is required since -> has higher priority

问题 I want to selectively link libm.a statically, all the other libraries ( libc.so included) dinamically. But if I use the math functions from math.h , it almost always fails to link correctly. Why? And why does it work sometimes? (For example if I only use sqrt , fabs or, strangely, tanh , it seems to link correctly) myscript.sh: #!/bin/bash for i in sqrt tanh sin tan do echo "-----$i----------" sed "s/ciao/$i/" prova.c >provat.c gcc provat.c -fno-builtin -l:libm.a [[ $? -eq 0 ]] && { echo -n "

问题 As the question states, what exactly are the implications of having the 'implicit declaration of function' warning? We just cranked up the warning flags on gcc and found quite a few instances of these warnings and I'm curious what type of problems this may have caused prior to fixing them? Also, why is this a warning and not an error. How is gcc even able to successfully link this executable? As you can see in the example below, the executable functions as expected. Take the following two

问题 I recently found that a fairly large image manipulation program I'm writing in C on a Windows 8 machine has a bug when used in very particular circumstances. Unfortunately, the bug is causing my entire computer to come to a standstill so that my only option is to pull the plug on the computer (especially annoying when I'm working remotely...) Because it's an image manipulation program, I can't just flood it with print statements to isolate the problematic section - the problem occurs

问题 While compiling my program which is using libevent library I am using gcc option -levent. But I am getting this error - /usr/bin/ld: cannot find -levent I do not have libevent on my system so I am statically linking to it while compiling using gcc -o Hello -static -I libevent-1.4.12-stable/ hello.c -levent How can i resolve this? Thanks in advance! 回答1: Where is the libevent.(a|so) file on your system? If it isn't on your system's library path then you will have to add a -L option adding its