Dynamic variable cpp compilation [duplicate]

问题

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g++ command line macro define byte stream (1 answer)

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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.

来源：https://stackoverflow.com/questions/50429180/dynamic-variable-cpp-compilation