strlen 与零长度字符串不一致

Question

I'm creating a DataStage parallel routine, which is a C or C++ function that is called from within IBM (formerly Ascential) DataStage. It is failing if one of the strings passed in is zero length. If I put this at the very first line of the function:

return strlen(str);

then it returns 0 for the calls that pass in empty values into str. If I put this at the first line, however...

if (strlen(str)==0) {return 0;}

then it does not return and goes into an infinite loop

I'm baffled - it works fine in a test harness, but not in DataStage.

Maybe there is something odd about the way DataStage passes empty strings to C routines?

int pxStrFirstCharList(char *str, char *chars )
{
  if (strlen(str)==0) {return 0;}
  if (strlen(chars)==0) {return 0;}
  int i = 0;
  //Start search
  while (str[i]) //for the complete input string
  {
    if (strchr(chars, str[i]))
    {
      return i+1;
    }
    ++i;
  }
  return 0;
}

Answer 1

There is a builtin function for what you are doing, it's called strcspn . This function takes two strings, and searches the first one for the first occurance of any of the characters of the second string.

I suggest using that than RYO...

http://www.cplusplus.com/reference/clibrary/cstring/strcspn/

Answer 2

I guess it is the strlen's issue when the length of the string is 0. For example,

char s1[0]; char *s2="a";

printf("%d %s\\n", sizeof(s1), s1);//0 @

printf("%d %s\\n", strlen(s1), s1);//3 @

printf("%d %s\\n", sizeof(s2), s2);//8 a

printf("%d %s\\n", strlen(s2), s2);// 1 a

You will get a weird answer for using strlen and you can check its source code in detail( https://code.woboq.org/userspace/glibc/string/strlen.c.html ). In nutshell, you can use sizeof instead of strlen for char string or avoid 0 length case by using strlen.

Answer 3

How about this?

int pxStrFirstCharList(char *str, char *chars )
{
  if (str && chars && (0 != strlen(str)) && (0 != strlen(chars)))
  {
    int i = 0;
    //Start search
    while (str[i]) //for the complete input string
    {
      if (strchr(chars, str[i]))
      {
        return i+1;
      }
      ++i;
    }
  }
  return 0;
}

Also, I don't quite get the point of the while loop ... (and no, I don't mean that this could be written as for ). What I mean is that on one hand you are doing a search ( strstr ) that itself will be implemented as a loop and still you have some outer loop. Could it be that you actually wanted to have chars in its place, ie:

int pxStrFirstCharList(char *str, char *chars )
{
  if (str && chars && (0 != strlen(str)) && (0 != strlen(chars)))
  {
    int i = 0;
    //Start search
    while (chars[i]) //for the complete input string
    {
      if (strchr(str, chars[i]))
      {
        return i+1;
      }
      ++i;
    }
  }
  return 0;
}

...? That is, look for each of the characters within chars inside the string denoted by str ...

Answer 4

If NULL is not explicitly part of the game, at least during development phase, it's always a good idea to add a precondition check on pointers received by a function:

int pxStrFirstCharList(char *str, char *chars )
{
  if (!str)
    return -1;

  if (!chars)
    return -2;
....

(The negative values -1 and -2 than tell the caller that something went wrong)

Or doing it in a more relaxed way, silently accepting NULL pointer strings as ""-string:

int pxStrFirstCharList(char *str, char *chars )
{
  if (!str)
    return 0;

  if (!chars)
    return 0;
...

If you are the only one using this API you could #ifndef BUILD_RELEASE these checks away for a release build if anything is tested stable.