How to use setenv() to export a variable in c++?

by

From the setenv() manual entry:

SYNOPSIS

#include <stdlib.h>  
int setenv(const char *envname, const char *envval, int overwrite);

DESCRIPTION
The setenv() function shall update or add a variable in the environment of the calling process. The envname argument points to a string containing the name of an environment variable to
be added or altered. The environment variable shall be set to the value to which envval points. The function shall fail if envname points to a string which contains an ‘=’ character. If
the environment variable named by envname already exists and the value of overwrite is non-zero, the function shall return success and the environment shall be updated. If the environment
variable named by envname already exists and the value of overwrite is zero, the function shall return success and the environment shall remain unchanged.

If the application modifies environ or the pointers to which it points, the behavior of setenv() is undefined. The setenv() function shall update the list of pointers to which environ
points.

The strings described by envname and envval are copied by this function.

The setenv() function need not be reentrant. A function that is not required to be reentrant is not required to be thread-safe.

RETURN VALUE
Upon successful completion, zero shall be returned. Otherwise, -1 shall be returned, errno set to indicate the error, and the environment shall be unchanged.

So you should call 

setenv("ROS_HOSTNAME","xxx",1); // does overwrite

or 

setenv("ROS_HOSTNAME","xxx",0); // does not overwrite

for your case. Depends, if you want to overwrite a possibly existing definition.

NOTE:

You can’t use setenv() to export variables from your process to the calling process (shell)!
Child processes created with fork, will inherit the current processes environment definitions, thus your changes and additions as well.

More Related Contents:

  1. Debugging with command-line parameters in Visual Studio
  2. How do I compile a Visual Studio project from the command-line?
  3. How can I execute external commands in C++/Linux?
  4. How to define a string literal in gcc command line?
  5. Create a function to check for key press in Unix using ncurses
  6. Getting another process command line in Windows
  7. How can I define a string literal on the GCC command line?
  8. Avoid memory leaks in C++ Pointers [closed]
  9. initializer_list and template type deduction
  10. How do I concatenate multiple C++ strings on one line?
  11. How many and which are the uses of “const” in C++?
  12. Why is the destructor of the class called twice?
  13. Is the pass-by-value-and-then-move construct a bad idiom?
  14. Portability of binary serialization of double/float type in C++
  15. Why is this code trying to call the copy constructor?
  16. Bigint (bigbit) library
  17. When should I use typedef in C++?
  18. How to use SQLite in a multi-threaded application?
  19. Simplest way to determine return type of function
  20. How do I prevent a class from being allocated via the ‘new’ operator? (I’d like to ensure my RAII class is always allocated on the stack.)
  21. How to make G++ preprocessor output a newline in a macro?
  22. Does delete work with pointers to base class?
  23. Program can’t find libgcc_s_dw2-1.dll [duplicate]
  24. When extending a padded struct, why can’t extra fields be placed in the tail padding?
  25. Converting bool to text in C++
  26. How can i estimate memory usage of std::map?
  27. When a float variable goes out of the float limits, what happens?
  28. OpenMP: What is the benefit of nesting parallelizations?
  29. how to assign multiple values into a struct at once?
  30. Is there a safe navigation operator for C++?

Leave a Comment