Difference between revisions of "cpp/utility/program/getenv"
From cppreference.com
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| − | {{cpp/title| getenv}} | + | {{cpp/title|getenv}} |
{{cpp/utility/program/navbar}} | {{cpp/utility/program/navbar}} | ||
| − | {{ddcl | header=cstdlib | | + | {{ddcl|header=cstdlib| |
char* getenv( const char* env_var ); | char* getenv( const char* env_var ); | ||
}} | }} | ||
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{{rev begin}} | {{rev begin}} | ||
{{rev|until=c++11| | {{rev|until=c++11| | ||
| − | This function is not required to be thread-safe. Another call to getenv, as well as a call to the POSIX functions [ | + | This function is not required to be thread-safe. Another call to {{tt|getenv}}, as well as a call to the POSIX functions [https://pubs.opengroup.org/onlinepubs/9699919799/functions/setenv.html {{tt|setenv()}}], [https://pubs.opengroup.org/onlinepubs/9699919799/functions/unsetenv.html {{tt|unsetenv()}}], and [https://pubs.opengroup.org/onlinepubs/9699919799/functions/putenv.html {{tt|putenv()}}] may invalidate the pointer returned by a previous call or modify the string obtained from a previous call. |
}} | }} | ||
{{rev|since=c++11| | {{rev|since=c++11| | ||
| − | This function is thread-safe (calling it from multiple threads does not introduce a data race) as long as no other function modifies the host environment. In particular, the POSIX functions [ | + | This function is thread-safe (calling it from multiple threads does not introduce a data race) as long as no other function modifies the host environment. In particular, the POSIX functions [https://pubs.opengroup.org/onlinepubs/9699919799/functions/setenv.html {{tt|setenv()}}], [https://pubs.opengroup.org/onlinepubs/9699919799/functions/unsetenv.html {{tt|unsetenv()}}], and [https://pubs.opengroup.org/onlinepubs/9699919799/functions/putenv.html {{tt|putenv()}}] would introduce a data race if called without synchronization. |
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{{rev end}} | {{rev end}} | ||
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===Parameters=== | ===Parameters=== | ||
{{par begin}} | {{par begin}} | ||
| − | {{par | env_var | null-terminated character string identifying the name of the environmental variable to look for }} | + | {{par|env_var|null-terminated character string identifying the name of the environmental variable to look for}} |
{{par end}} | {{par end}} | ||
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===Notes=== | ===Notes=== | ||
| − | On POSIX systems, the [ | + | On POSIX systems, the [https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap08.html#tag_08 environment variables] are also accessible through the global variable {{tt|environ}}, declared as {{c|extern char** environ;}} in {{header|unistd.h|<!--to skip red-link generation-->lang=c}}, and through the optional third argument, {{tt|envp}}, of [[cpp/language/main function|the main function]]. |
===Example=== | ===Example=== | ||
{{example | {{example | ||
| − | + | |code= | |
| − | + | ||
| − | + | ||
#include <cstdlib> | #include <cstdlib> | ||
| + | #include <iostream> | ||
int main() | int main() | ||
{ | { | ||
| − | if(const char* env_p = std::getenv("PATH")) | + | if (const char* env_p = std::getenv("PATH")) |
std::cout << "Your PATH is: " << env_p << '\n'; | std::cout << "Your PATH is: " << env_p << '\n'; | ||
} | } | ||
| − | + | |p=true | |
| + | |output= | ||
Your PATH is: /usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games | Your PATH is: /usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games | ||
}} | }} | ||
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===See also=== | ===See also=== | ||
{{dsc begin}} | {{dsc begin}} | ||
| − | {{dsc see c | c/program/getenv}} | + | {{dsc see c|c/program/getenv}} |
{{dsc end}} | {{dsc end}} | ||
{{langlinks|de|es|fr|it|ja|pt|ru|zh}} | {{langlinks|de|es|fr|it|ja|pt|ru|zh}} | ||
Latest revision as of 12:34, 13 October 2023
| Defined in header <cstdlib>
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| char* getenv( const char* env_var ); |
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Searches the environment list provided by the host environment (the OS), for a string that matches the C string pointed to by env_var and returns a pointer to the C string that is associated with the matched environment list member.
|
This function is not required to be thread-safe. Another call to |
(until C++11) |
|
This function is thread-safe (calling it from multiple threads does not introduce a data race) as long as no other function modifies the host environment. In particular, the POSIX functions |
(since C++11) |
Modifying the string returned by getenv invokes undefined behavior.
Contents |
[edit] Parameters
| env_var | - | null-terminated character string identifying the name of the environmental variable to look for |
[edit] Return value
Character string identifying the value of the environmental variable or null pointer if such variable is not found.
[edit] Notes
On POSIX systems, the environment variables are also accessible through the global variable environ, declared as extern char** environ; in <unistd.h>, and through the optional third argument, envp, of the main function.
[edit] Example
Run this code
#include <cstdlib> #include <iostream> int main() { if (const char* env_p = std::getenv("PATH")) std::cout << "Your PATH is: " << env_p << '\n'; }
Possible output:
Your PATH is: /usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games
[edit] See also
| C documentation for getenv
|
