Movatterモバイル変換

[0]ホーム
URL:

cppreference.com
Namespaces
Variants
    Actions

      getenv, getenv_s

      From cppreference.com
      <c‎ |program
       
       
      Program support utilities
      Program termination
      Unreachable control flow
      Communicating with the environment
      getenvgetenv_s
      (C11)
      Memory alignment query
      Signals
      Signal types
      Non-local jumps
      Types
       
      Defined in header<stdlib.h>
      char*getenv(constchar*name);
      		 (1)
      errno_t getenv_s(size_t*restrict len,char*restrict value,
                        rsize_t valuesz,constchar*restrict name);
      		 (2)(since C11)
      1) Searches for an environmental variable with namename 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 togetenv, as well as a call to the POSIX functionssetenv(),unsetenv(), andputenv() may invalidate the pointer returned by a previous call or modify the string obtained from a previous call.
      Modifying the string returned bygetenv invokes undefined behavior.
      2) Same as(1), except that the values of the environment variable is written to the user-provided buffervalue (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 tovalue[0] (unless null). In addition, the following errors are detected at runtime and call the currently installedconstraint handler function:
      • name is a null pointer
      • valuesz is greater thanRSIZE_MAX
      • value is a null pointer andvaluesz is not zero
      As with all bounds-checked functions,getenv_s is 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 constant1 before including<stdlib.h>.

      Contents

      [edit]Parameters

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

      [edit]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 (unlesslen is a null pointer).

      [edit]Notes

      On POSIX systems, theenvironment variables are also accessible through the global variableenviron, declared asexternchar**environ; in<unistd.h>, and through the optional third argument,envp, ofthe main function.

      The call togetenv_s with a null pointer forvalue and zero forvaluesz is used to determine the size of the buffer required to hold the entire result.

      [edit]Example

      Run this code
      #include <stdio.h>#include <stdlib.h> int main(void){constchar*name="PATH";constchar*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

      [edit]References

      • C23 standard (ISO/IEC 9899:2024):
      • 7.22.4.6 The getenv function (p: TBD)
      • K.3.6.2.1 The getenv_s function (p: TBD)
      • C17 standard (ISO/IEC 9899:2018):
      • 7.22.4.6 The getenv function (p: 256-257)
      • K.3.6.2.1 The getenv_s function (p: 440-441)
      • C11 standard (ISO/IEC 9899:2011):
      • 7.22.4.6 The getenv function (p: 352-353)
      • K.3.6.2.1 The getenv_s function (p: 606-607)
      • C99 standard (ISO/IEC 9899:1999):
      • 7.20.4.5 The getenv function (p: 317)
      • C89/C90 standard (ISO/IEC 9899:1990):
      • 4.10.4.4 The getenv function

      [edit]See also

      Retrieved from "https://en.cppreference.com/mwiki/index.php?title=c/program/getenv&oldid=160652"
      [8]ページ先頭
      ©2009-2025 Movatter.jp