ifndef

Multiple definition of namespace::variable even using ifndef

由 十年热恋 提交于 2021-02-19 07:40:07
问题 I know I must be doing something wrong here. rank.h #ifndef RANK_H #define RANK_H namespace mmi { int chunk; void rank(int my_rank); } #endif rank.cpp #include "rank.h" namespace mmi { //do something with chunk } main.cpp #include "rank.h" int main() { mmi::chunk = 1; } And the output of compilation; g++ -g -Wall -std=gnu++11 -c -o main.o main.cpp g++ -g -Wall -std=gnu++11 -c -o rank.o rank.cpp mpic++ main.o rank.o -o main rank.o:(.bss+0x0): multiple definition of `mmi::chunk' main.o:(.bss

Why only define a macro if it's not already defined?

由 僤鯓⒐⒋嵵緔 提交于 2019-12-05 08:20:15
问题 All across our C code base, I see every macro defined the following way: #ifndef BEEPTRIM_PITCH_RATE_DEGPS #define BEEPTRIM_PITCH_RATE_DEGPS 0.2f #endif #ifndef BEEPTRIM_ROLL_RATE_DEGPS #define BEEPTRIM_ROLL_RATE_DEGPS 0.2f #endif #ifndef FORCETRIMRELEASE_HOLD_TIME_MS #define FORCETRIMRELEASE_HOLD_TIME_MS 1000.0f #endif #ifndef TRIMSYSTEM_SHEARPIN_BREAKINGFORCE_LBS #define TRIMSYSTEM_SHEARPIN_BREAKINGFORCE_LBS 50.0f #endif What is the rationale of doing these define checks instead of just

Why only define a macro if it's not already defined?

由 依然范特西╮ 提交于 2019-12-03 22:01:18
All across our C code base, I see every macro defined the following way: #ifndef BEEPTRIM_PITCH_RATE_DEGPS #define BEEPTRIM_PITCH_RATE_DEGPS 0.2f #endif #ifndef BEEPTRIM_ROLL_RATE_DEGPS #define BEEPTRIM_ROLL_RATE_DEGPS 0.2f #endif #ifndef FORCETRIMRELEASE_HOLD_TIME_MS #define FORCETRIMRELEASE_HOLD_TIME_MS 1000.0f #endif #ifndef TRIMSYSTEM_SHEARPIN_BREAKINGFORCE_LBS #define TRIMSYSTEM_SHEARPIN_BREAKINGFORCE_LBS 50.0f #endif What is the rationale of doing these define checks instead of just defining the macros? #define BEEPTRIM_PITCH_RATE_DEGPS 0.2f #define BEEPTRIM_ROLL_RATE_DEGPS 0.2f #define

Preprocessor #ifndef

由 淺唱寂寞╮ 提交于 2019-12-01 13:51:18
Assume I have a.h which includes the following: <stdbool.h> <stddef.h> <stdin.h> Assume I also have b.h which also includes <stdbool.h> . If a.h has the #ifndef preprocessor definition statement in it and b.h doesn't. Will a.h include only what hasn't been included in b.h ? So when b.h includes a.h , will a.h include stddef.h and stein.h and not re-include stdbool.h or are those preprocessor definition functions only used to see whether this whole class is redefined, and not specific functions within it? EDIT: Also, assume b.h includes another header file which includes stdbool.h -that makes b

Preprocessor #ifndef

由 北慕城南 提交于 2019-12-01 12:53:24
问题 Assume I have a.h which includes the following: <stdbool.h> <stddef.h> <stdin.h> Assume I also have b.h which also includes <stdbool.h> . If a.h has the #ifndef preprocessor definition statement in it and b.h doesn't. Will a.h include only what hasn't been included in b.h ? So when b.h includes a.h , will a.h include stddef.h and stein.h and not re-include stdbool.h or are those preprocessor definition functions only used to see whether this whole class is redefined, and not specific
订阅 ifndef