给定一个计数字符串(字符数组,或像std::string
这样的包装器),在C或c++中是否有一种"适当"的方式来转义和/或反转义它,使得"特殊"字符(如null字符)成为C风格转义和"正常"字符保持原样?
还是我必须手工做?
处理单个字符的函数:
/*
** Does not generate hex character constants.
** Always generates triple-digit octal constants.
** Always generates escapes in preference to octal.
** Escape question mark to ensure no trigraphs are generated by repetitive use.
** Handling of 0x80..0xFF is locale-dependent (might be octal, might be literal).
*/
void chr_cstrlit(unsigned char u, char *buffer, size_t buflen)
{
if (buflen < 2)
*buffer = ' ';
else if (isprint(u) && u != ''' && u != '"' && u != '\' && u != '?')
sprintf(buffer, "%c", u);
else if (buflen < 3)
*buffer = ' ';
else
{
switch (u)
{
case 'a': strcpy(buffer, "\a"); break;
case 'b': strcpy(buffer, "\b"); break;
case 'f': strcpy(buffer, "\f"); break;
case 'n': strcpy(buffer, "\n"); break;
case 'r': strcpy(buffer, "\r"); break;
case 't': strcpy(buffer, "\t"); break;
case 'v': strcpy(buffer, "\v"); break;
case '\': strcpy(buffer, "\\"); break;
case ''': strcpy(buffer, "\'"); break;
case '"': strcpy(buffer, "\""); break;
case '?': strcpy(buffer, "\?"); break;
default:
if (buflen < 5)
*buffer = ' ';
else
sprintf(buffer, "\%03o", u);
break;
}
}
}
下面是处理以null结尾的字符串的代码(使用上面的函数):
void str_cstrlit(const char *str, char *buffer, size_t buflen)
{
unsigned char u;
size_t len;
while ((u = (unsigned char)*str++) != ' ')
{
chr_cstrlit(u, buffer, buflen);
if ((len = strlen(buffer)) == 0)
return;
buffer += len;
buflen -= len;
}
*buffer = ' ';
}
比起分配一个新的缓冲区来包含转义字符串,我更喜欢在将字符串写入流时转义字符串。
下面的函数使代码简洁易读。
struct Escaped
{
const char* str;
friend inline std::ostream& operator<<(std::ostream& os, const Escaped& e)
{
for (const char* char_p = e.str; *char_p != ' '; char_p++)
{
switch (*char_p)
{
case 'a': os << "\a"; break;
case 'b': os << "\b"; break;
case 'f': os << "\f"; break;
case 'n': os << "\n"; break;
case 'r': os << "\r"; break;
case 't': os << "\t"; break;
case 'v': os << "\v"; break;
case '\': os << "\\"; break;
case ''': os << "\'"; break;
case '"': os << "\""; break;
case '?': os << "\?"; break;
default: os << *char_p;
}
}
return os;
}
};
int main()
{
std::cout << Escaped{ "foontbar" } << std::endl;
}
生产
foon bar
//convert 'n' literal to escape code for 'n'
#define STRING "hello\\nworld\n"
char *p = malloc(strlen(STRING) + 1);
strcpy(p,STRING);
char *s = p;
char c;
for(;*p;++p)
{
while(*p == '\')
{
++p;
switch(*p){
case '\':
c = '\';
goto gstat;
case 'n':
c = 'n';
default:
{
gstat:
strcpy(p-1,p);
*(p-1) = c;
}
break;
}
}
}
printf("%s",s);