CODEWITHSUNDEEP
cstrdup
Sparks_Fly
Sparks_Fly

Reputation: 439

error: conflicting types for 'strdup'!

This is program in book “The c programming language”.
There is an error:conflicting types for 'strdup'! When encounter function 'strdup'.But if you change 'strdup' to other name, for example 'strdu', the error will disappear.
I don't know WHY？ By the way, I use code::blocks as my IDE.

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

#define MAXWORD 100

struct tnode {
    char *word;           
    int count;           
    struct tnode *left;   
    struct tnode *right; 
};

struct tnode *addtree(struct tnode *, char *);
struct tnode *talloc(void);

void treeprint(struct tnode *);
int getword(char *, int);
char *strdup(char *);

/*  word frequency count */
int main()
{
    struct tnode *root;
    char word[MAXWORD];

    root = NULL;
    while (getword(word, MAXWORD) != EOF)
        if (isalpha(word[0]))
            root = addtree(root, word);
    treeprint(root);
    return 0;
}
/* addtree: add a node with w, at or below p */
struct tnode *addtree(struct tnode *p, char *w)
{
    int cond;
    if (p == NULL) {       /* a new word has arrived */
        p = talloc();      /* make a new node */
        p->word = strdup(w);
        p->count = 1;
        p->left = p->right = NULL;
    } else if ((cond = strcmp(w, p->word)) == 0)
        p->count++;        /* repeated word */
    else if (cond < 0)     /* less than into left subtree */
        p->left = addtree(p->left, w);
    else                   /* greater than into right subtree */
        p->right = addtree(p->right, w);
    return p;
};

/* treeprint: in-order print of tree p */
void treeprint(struct tnode *p)
{
    if (p != NULL) {
        treeprint(p->left);
        printf("%4d %s\n", p->count, p->word);
        treeprint(p->right);
    }
}

/* talloc: make a tnode */
struct tnode *talloc(void)
{
    return (struct tnode *) malloc(sizeof(struct tnode));
};

char *strdup(char *s)  /* make a duplicate of s */
{
    char *p;

    p = (char *) malloc(sizeof(strlen(s)) + 1);
    if (p != NULL)
        strcmp(p, s);
    return p;
}
.... some other function ....

Upvotes: 2

Views: 2299

Answers (2)

unwind
unwind

Reputation: 399949

You cannot have a function of your own whose name starts with str. That whole "namespace" is reserved, in C.

In this case, strdup() is a standard function from <string.h>, which your function declaration collides with.

Note that it's not enough to stop using <string.h>, the name is still reserved so you cannot validly use it.

A couple of further notes:

  1. The input is not written to, so it should be a const pointer.
  2. Please don't cast the return value of malloc() in C.
  3. Your strdup() workalike is horribly broken, it calls strcmp() when it means strcpy().
  4. Your use of sizeof(strlen(s)) is totally wrong and will cause massive problems even if you fix the strcmp()/strcpy() problem.

A reasonable strdup() implementation is:

char * my_strdup(const char *s)
{
  char *r = NULL;
  if(s != NULL)
  {
    const size_t size = strlen(s) + 1;
    if((r = malloc(size)) != NULL)
      memcpy(r, s, size);
  }
  return r;
}

I use memcpy() since I know the length, it can be quicker.

Upvotes: 7

Ilie NEACSU
Ilie NEACSU

Reputation: 550

strdup is allready defined in string.h. Just rename your function.

Upvotes: 2

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