C：如何将命令行的特殊字符捕获为字符串

Question

I would like to capture special characters such as \\n from the command line into a C program.

For example, for the following program, if I run ./a.out "\\nfoo\\n" , I'd like to to print (newline) foo (newline) instead of "\\nfoo\\n". How can I capture that in to a string?

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

int main(int argc, char ** argv){
    if(argc >1){
        char * s = strdup(argv[1]);
        printf("%s\n", s);
        free(s);
    }
    return 0;
}

Edit: sorry, by (newline) foo (newline), I mean the acutal output is

foo

Currently,the output is literally "\\nabc\\n".(newlines are not printed because s captures "\\n" 2 characters instead of the '\\n' character). Sorry about the confusion.

Answer 1

make a new string, iterate through the old string adding characters to the new string. if you ever see the '\\' character, add a special character to the new string based on the next character in the old string.

Answer 2

C strings cannot grow dynamically, so you will need to allocate space for a new string and fill it with the desired contents. But to know how many characters will be required, you need to make a pass over *s first and count. Once you count the number of characters needed, you can malloc space for a new string, and start iterating over the old string and copying characters. Whenever you encounter one of your "special" characters, copy the appropriate replacement string into the new string.

Some code sketches (not tested; if you want to use any of this, you'll have to test and debug yourself):

char* replacement(char c) {
  if(c == '\n')
    return "(newline)";
  else if(c == '\t')
    return "(tab)";
  else
    return NULL;
}

int charactersNeeded(char* s) {
  int count = 0;
  char* r;
  while(*s != '\0') {
    r = replacement(*s);
    if(r != NULL)
      count += strlen(r);
    else
      count++;
    s++;
  }
  return count;
}

void copyString(char* s, char* t) {
  /* it is assumed that t points to a buffer of sufficient length
     to hold all the copied chars, as well as terminating null */
  char* r;
  do {
    r = replacement(*s);
    if(r != NULL) {
      strcpy(t, d);
      t += strlen(d)-1;
    } else *t = *s;
    s++;
    t++;
  } while(*s != '\0');
}