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C99 defines {{getenv()}} to have the following behavior: \[[ISO/IEC 9899:1999|AA. C References#ISO/IEC 9899-1999]\] |
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Windows provides the [{{getenv_s()}} and {{\_wgetenv_s()}}|http://msdn.microsoft.com/en-us/library/tb2sfw2z(VS.80).aspx] functions for getting a value from the current environment \[[MSDN|AA. C References#MSDN]\]. |
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char *tmpvar;
char *tempvar;
size_t requiredSize;
getenv_s(&requiredSize, NULL, 0, "TMP");
tmpvar = (char *)malloc(requiredSize * sizeof(char));
if (!tmpvar) {
/* Handle error */
}
getenv_s(&requiredSize, tmpvar, requiredSize, "TMP" );
getenv_s(&requiredSize, NULL, 0, "TEMP");
tempvar = (char *)malloc(requiredSize * sizeof(char));
if (!tempvar) {
free(tmpvar);
tmpvar = NULL;
/* Handle error */
}
getenv_s(&requiredSize, tempvar, requiredSize, "TEMP" );
if (strcmp(tmpvar, tempvar) == 0) {
if (puts("TMP and TEMP are the same.\n") == EOF) {
/* Handle error */
}
}
else {
if (puts("TMP and TEMP are NOT the same.\n") == EOF) {
/* Handle Error */
}
}
free(tmpvar);
tmpvar = NULL;
free(tempvar);
tempvar = NULL;
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Windows also provides the [{{\_dupenv_s()}} and {{\_wdupenv_s()}}|http://msdn.microsoft.com/en-us/library/ms175774.aspx] functions for getting a value from the current environment \[[MSDN|AA. C References#MSDN]\]. |
The _dupenv_s() function searches the list of environment variables for a specified name. If the name is found, a buffer is allocated, the variable's value is copied into the buffer, and the buffer's address and number of elements are returned. By allocating the buffer itself, _dupenv_s() and _wdupenv_s() provide a more convenient alternative to getenv_s() and _wgetenv_s().
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POSIX provides the [{{strdup()}}|http://www.opengroup.org/onlinepubs/009695399/functions/strdup.html] function, which can make a copy of the environment variable string \[[Open Group 04|AA. C References#Open Group 04]\]. The {{strdup()}} function is also included in ISO/IEC PDTR 24731-2 \[[ISO/IEC PDTR 24731-2|AA. C References#ISO/IEC ISO/IEC PDTR 24731-2]\]. |
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\[[ISO/IEC 9899:1999|AA. C References#ISO/IEC 9899-1999]\] Section 7.20.4, "Communication with the environment"
\[[ISO/IEC PDTR 24731-2|AA. C References#ISO/IEC PDTR 24731-2-2007]\]
\[[MSDN|AA. C References#MSDN]\] [{{\_dupenv_s()}} and {{\_wdupenv_s()}}|http://msdn.microsoft.com/en-us/library/ms175774.aspx], [{{getenv_s()}}, {{\_wgetenv_s()}}|http://msdn.microsoft.com/en-us/library/tb2sfw2z(VS.80).aspx]
\[[Open Group 04|AA. C References#Open Group 04]\] Chapter 8, and "Environment Variables", [{{strdup}}|http://www.opengroup.org/onlinepubs/009695399/functions/strdup.html]
\[[Viega 03|AA. C References#Viega 03]\] Section 3.6, "Using Environment Variables Securely" |
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