locale
char setlocale(int category, const char locale) locale == "", set according to ENV locale == NULL, query current
setlocale(LC_ALL, ""); //program made portable
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文件与目录 判断文件存在 文件大小 文件读取 文件写入
option
struct option { char name; int has_arg; int flag; int val; }
extern char *optarg; extern int optind, opterr, optopt;
int getopt_long(int argc, char **argv, char lopts, option lopts, int *longindex);
如果选项合法,返回选项 如果选项不合法,返回 '?'