source: asp3_tinet_ecnl_arm/trunk/musl-1.1.18/src/env/setenv.c@ 352

#include <stdlib.h>
#include <string.h>
#include <errno.h>

char *__strchrnul(const char *, int);
int __putenv(char *, size_t, char *);

void __env_rm_add(char *old, char *new)
{
        static char **env_alloced;
        static size_t env_alloced_n;
        for (size_t i=0; i < env_alloced_n; i++)
                if (env_alloced[i] == old) {
                        env_alloced[i] = new;
                        free(old);
                        return;
                } else if (!env_alloced[i] && new) {
                        env_alloced[i] = new;
                        new = 0;
                }
        if (!new) return;
        char **t = realloc(env_alloced, sizeof *t * (env_alloced_n+1));
        if (!t) return;
        (env_alloced = t)[env_alloced_n++] = new;
}

int setenv(const char *var, const char *value, int overwrite)
{
        char *s;
        size_t l1, l2;

        if (!var || !(l1 = __strchrnul(var, '=') - var) || var[l1]) {
                errno = EINVAL;
                return -1;
        }
        if (!overwrite && getenv(var)) return 0;

        l2 = strlen(value);
        s = malloc(l1+l2+2);
        if (!s) return -1;
        memcpy(s, var, l1);
        s[l1] = '=';
        memcpy(s+l1+1, value, l2+1);
        return __putenv(s, l1, s);
}