Dynamic variable cpp compilation [duplicate]

问题:

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• g++ command line macro define byte stream 1 answer

I wish I could edit a variable in a .h file since compilation Example:

#include <iostream> #include <stdlib.h>  #define HOST (char *)"http://localhost/" #define PATH "insert" 

I want to edite HOST from compilation like this:

g++ -o output source.cpp -HOST http://mywebsite/ 

回答1:

You can easily do that with something like this:

#include <iostream> #include <stdlib.h>  #ifndef HOST   #define HOST (char*)"http://localhost/" #endif  #define PATH "insert" 

Then, on the command-line, you either specify '-DHOST=(char*)"whatever"' (and it will be used), or do not pass in any -DHOST= flag, and the default in the header will be used.

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