字符串和16进制字符串的相互转化

我们在工作中，有时候会需要将字符串转化为16进制字符串给用户，因为ASCII中有些字符，当我们使用printf("%s",p_ch);输出时会杂乱无章，如果采用16进制，会好很多。

因此编写程序，代码如下：

#include <stdio.h>
#include <string.h>

int strToHex(char *ch, char *hex);
int hexToStr(char *hex, char *ch);
int hexCharToValue(const char ch);
char valueToHexCh(const int value);
int main(int argc, char *argv[])
{
    char ch[1024];
    char hex[1024];
    char result[1024];
    char *p_ch = ch;
    char *p_hex = hex;
    char *p_result = result;
    printf("please input the string:");
    scanf("%s",p_ch);

    strToHex(p_ch,p_hex);
    printf("the hex is:%s
",p_hex);
    hexToStr(p_hex, p_result);
    printf("the string is:%s
", p_result);
    return 0;
}

int strToHex(char *ch, char *hex)
{
  int high,low;
  int tmp = 0;
  if(ch == NULL || hex == NULL){
    return -1;
  }

  if(strlen(ch) == 0){
    return -2;
  }

  while(*ch){
    tmp = (int)*ch;
    high = tmp >> 4;
    low = tmp & 15;
    *hex++ = valueToHexCh(high); //先写高字节
    *hex++ = valueToHexCh(low); //其次写低字节
    ch++;
  }
  *hex = '';
  return 0;
}

int hexToStr(char *hex, char *ch)
{
  int high,low;
  int tmp = 0;
  if(hex == NULL || ch == NULL){
    return -1;
  }

  if(strlen(hex) %2 == 1){
    return -2;
  }

  while(*hex){
    high = hexCharToValue(*hex);
    if(high < 0){
      *ch = '';
      return -3;
    }
    hex++; //指针移动到下一个字符上
    low = hexCharToValue(*hex);
    if(low < 0){
      *ch = '';
      return -3;
    }
    tmp = (high << 4) + low;
    *ch++ = (char)tmp;
    hex++;
  }
  *ch = '';
  return 0;
}

int hexCharToValue(const char ch){
  int result = 0;
  //获取16进制的高字节位数据
  if(ch >= '0' && ch <= '9'){
    result = (int)(ch - '0');
  }
  else if(ch >= 'a' && ch <= 'z'){
    result = (int)(ch - 'a') + 10;
  }
  else if(ch >= 'A' && ch <= 'Z'){
    result = (int)(ch - 'A') + 10;
  }
  else{
    result = -1;
  }
  return result;
}

char valueToHexCh(const int value)
{
  char result = '';
  if(value >= 0 && value <= 9){
    result = (char)(value + 48); //48为ascii编码的‘0’字符编码值
  }
  else if(value >= 10 && value <= 15){
    result = (char)(value - 10 + 65); //减去10则找出其在16进制的偏移量，65为ascii的'A'的字符编码值
  }
  else{
    ;
  }

  return result;
}