Problem - Kevin Tafuro

value of an environment variable actually changes it. If you use the code from Recipe
1.1, you can be reasonably certain that there is only one environment variable for
each name.
Instead of using putenv( ) to modify the value of an environment variable, use spc_
putenv( ), shown in the following code. It will properly handle an environment as the
code in Recipe 1.1 builds it, as well as an unaltered environment. In addition to modifying
the value of an environment variable, spc_putenv( ) is also capable of adding
new environment variables.
We have not copied putenv( )’s signature with spc_putenv( ). If you use putenv( ),
you must pass it a string of the form “NAME=VALUE”. If you use spc_putenv( ), you
must pass it two strings; the first string is the name of the environment variable to
modify or add, and the second is the value to assign to the environment variable. If
an error occurs, spc_putenv( ) will return –1; otherwise, it will return 0.
Note that the following code is not thread-safe. You need to explicitly avoid the possibility
of manipulating the environment from two separate threads at the same time.
#include
#include
static int spc_environ;
int spc_putenv(const char *name, const char *value) {
int del = 0, envc, i, mod = -1;
char *envptr, **new_environ;
size_t delsz = 0, envsz = 0, namelen, valuelen;
extern char **environ;
/* First compute the amount of memory required for the new environment */
namelen = strlen(name);
valuelen = strlen(value);
for (envc = 0; environ[envc]; envc++) {
if (!strncmp(environ[envc], name, namelen) && environ[envc][namelen] = = '=') {
if (mod = = -1) mod = envc;
else {
del++;
delsz += strlen(environ[envc]) + 1;
}
}
envsz += strlen(environ[envc]) + 1;
}
if (mod = = -1) {
envc++;
envsz += (namelen + valuelen + 1 + 1);
}
envc -= del; /* account for duplicate entries of the same name */
envsz -= delsz;
/* allocate memory for the new environment */
envsz += (sizeof(char *) * (envc + 1));
94 | Chapter 3: Input Validation
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