Linux下有两个函数用来查询和设置环境变量

char *getenv(const char *name);

int putenv(const char *string);

getenv用于查询指定的环境变量的值，成功则返回该值，否则返回null。

putenv以一个键值对的格式设置给定的环境变量的值

1 #include 
     
       2 #include 
      
        3 #include 
       
         4  5 int main(int argc, char **argv) 6 { 7     char *var, *value; 8      9     if(argc == 1 || argc > 3)10     {11         fprintf(stderr, "usage:environ var [value]\n");12         exit(-1);13     }14 15     var = argv[1];16     value = getenv(var);17     if(value)18     {19         printf("Variable %s has value %s\n", var, value);20     }21     else22     {23         printf("Variable %s has no value\n");24     }25     26     if(argc == 3)27     {28         char *string;29         value = argv[2];30         string = malloc(strlen(var) + strlen(value) + 2);31         if(!string)32         {33             fprintf(stderr, "out of memory\n");34             exit(1);35         }36         strcpy(string, var);37         strcat(string, "=");38         strcat(string, value);39         printf("calling putenv with: %s\n", string);40         if(putenv(string) != 0)41         {42             fprintf(stderr, "putenv failed\n");43             free(string);44             exit(1);45         }46         47         value = getenv(var);48         if(value)49         {50             printf("New value of %s is %s\n", var, value);51         }52         else53         {54             printf("New value of %s is null??\n", var);55         }56         57         return 0;58     }59 }