From 754bbf7a25a8dda49b5d08ef0d0443bbf5af0e36 Mon Sep 17 00:00:00 2001 From: Craig Jennings Date: Sun, 7 Apr 2024 13:41:34 -0500 Subject: new repository --- devdocs/c/program%2Fgetenv.html | 62 +++++++++++++++++++++++++++++++++++++++++ 1 file changed, 62 insertions(+) create mode 100644 devdocs/c/program%2Fgetenv.html (limited to 'devdocs/c/program%2Fgetenv.html') diff --git a/devdocs/c/program%2Fgetenv.html b/devdocs/c/program%2Fgetenv.html new file mode 100644 index 00000000..912fe7b3 --- /dev/null +++ b/devdocs/c/program%2Fgetenv.html @@ -0,0 +1,62 @@ +

getenv, getenv_s

Defined in header <stdlib.h> 
char *getenv( const char *name );
+		 (1) 
errno_t getenv_s( size_t *restrict len, char *restrict value,
+                  rsize_t valuesz, const char *restrict name );
+		 (2) (since C11)
+1) Searches for an environmental variable with name name in the host-specified environment list and returns a pointer to the string that is associated with the matched environment variable. The set of environmental variables and methods of altering it are implementation-defined.
+ This function is not required to be thread-safe. Another call to getenv, as well as a call to the POSIX functions setenv(), unsetenv(), and putenv() may invalidate the pointer returned by a previous call or modify the string obtained from a previous call.
+ Modifying the string returned by getenv invokes undefined behavior.
+2) Same as (1), except that the values of the environment variable is written to the user-provided buffer value (unless null) and the number of bytes written is stored in the user-provided location *len (unless null). If the environment variable is not set in the environment, zero is written to *len (unless null) and '\0' is written to value[0] (unless null). In addition, the following errors are detected at runtime and call the currently installed constraint handler function:
+
+
    +
  • name is a null pointer
    • +
  • valuesz is greater than RSIZE_MAX
    • +
  • value is a null pointer and valuesz is not zero
    • +
+
As with all bounds-checked functions, getenv_s only guaranteed to be available if __STDC_LIB_EXT1__ is defined by the implementation and if the user defines __STDC_WANT_LIB_EXT1__ to the integer constant 1 before including <stdlib.h>.
+
+

Parameters

+ + + + +
name - null-terminated character string identifying the name of the environmental variable to look for
len - pointer to a user-provided location where getenv_s will store the length of the environment variable
value - pointer to a user-provided character array where getenv_s will store the contents of the environment variable
valuesz - maximum number of characters that getenv_s is allowed to write to dest (size of the buffer)

Return value

+1) character string identifying the value of the environmental variable or null pointer if such variable is not found.
+2) zero if the environment variable was found, non-zero if it was not found or if a runtime constraint violation occurred. On any error, writes zero to *len (unless len is a null pointer).

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.

+

The call to getenv_s with a null pointer for value and zero for valuesz is used to determine the size of the buffer required to hold the entire result.

+

Example

#include <stdio.h>
+#include <stdlib.h>
+ 
+int main(void)
+{
+    const char *name = "PATH";
+    const char *env_p = getenv(name);
+    if (env_p)
+        printf("Your %s is %s\n", name, env_p);
+}

Possible output:

+
Your PATH is /home/gamer/.local/bin:/usr/local/bin:/usr/bin:/bin:/usr/share/games

References

See also

+
C++ documentation for getenv
+

+ © cppreference.com
Licensed under the Creative Commons Attribution-ShareAlike Unported License v3.0.
+ https://en.cppreference.com/w/c/program/getenv +

+
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