减少库的使用，解决那些需要小代码量，但苦恼于没有简易的字符串处理函数的郁闷
char *itoa_private(int val, char *buf, unsigned radix);//整数转字符串
int my_isdigit(int ch);//判断字符是否为数字
long long StrToInt(const char *s,int sign);//字符串转数字
int atoi_32(const char *s);//将字符串str转换为32位整型，其正数的最值为0x7FFFFFFF，负数的最小值为0x80000000,考虑数字会溢出的情况
void LettersChange(unsigned char*str, unsigned char font);//大小写字母变成大小写字母
signed int st_strlen(unsigned char* str);//获取字符串长度
signed int st_strcmp(unsigned char *s,unsigned char *t);//比较两个字符串大小
unsigned char *st_strcpy(unsigned char *t,unsigned char *s);//字符串拷贝
signed int st_strncmp(unsigned char *dest,unsigned char *src,unsigned int Len);//可变长度字符串大小比较
signed char st_toupper(unsigned char c);//小写字符转化为大写字符
unsigned char *st_strcat(unsigned char *s,unsigned char *t);//字符串连接
signed int st_memcpy(unsigned char *dest, unsigned char *src, unsigned int Len);//可变长度内存拷贝
signed int st_memset(unsigned char *dest,unsigned char byte, unsigned int Len);//设置长度为Len的内存块为byte
signed int st_memcmp(unsigned char* dest, unsigned char* src, unsigned int Len);//内存段内数据比较
int gsmInvertNumbers(const char* pSrc, char* pDst, int nSrcLength);//正常顺序的字符串转换为两两颠倒的字符串，若长度为奇数，补'F'凑成偶数
int gsmSerializeNumbers(const char* pSrc, char* pDst, int nSrcLength);//两两颠倒的字符串转换为正常顺序的字符串
int gsmEncode7bit(const char* pSrc, unsigned char* pDst, int nSrcLength);//7bit编码
int gsmDecode7bit(const unsigned char* pSrc, char* pDst, int nSrcLength);//7bit解码
int gsmString2Bytes(const char* pSrc, unsigned char* pDst, int nSrcLength);//可打印字符串转换为字节数据
int gsmBytes2String(const unsigned char* pSrc, char* pDst, int nSrcLength);//字节数据转换为可打印字符串
