c-我不能对函数返回的char指针使用free()

Question

我无法清除在ft_itoa_base()函数中分配的str变量。错误pointer being freed was not allocated。

void            work_ptr_accuracy(t_args *args, char **return_str, 
va_list *arg)
{
int                     size_accuracy;
char                    *str_tmp;
char                    *str;
unsigned long long int  n;
str_tmp = NULL;
str = NULL;
if (args->accuracy != -1)
{
size_accuracy = args->accuracy;
n = va_arg(*arg, unsigned long long int);
str = ft_itoa_base(n, 16, LOWERCASE);
*return_str = ft_substr(str, 0, size_accuracy);
free(str);
str_tmp = ft_strjoin("0x", *return_str);
free(*return_str);
*return_str = str_tmp;
}
}

这是ft_itoa_base()

char        *ft_itoa_base(unsigned long long int value, 
unsigned long long int base, int regist)
{
int                     len;
unsigned long long int  digit;
char                    *return_str;
char                    *base_tmp;
base_tmp = get_register(regist);
if (value == 0)
return ("0");
len = 0;
digit = value;
ft_baselen(digit, base, &len);  
if (!(return_str = (char *)malloc(sizeof(char) * (len + 1))))
return (NULL);
return_str[len] = '';
while (digit)
{
return_str[--len] = base_tmp[digit % base];
digit /= base;
}
if (value < 0 && base == 10)
return_str[0] = '-';
return (return_str);
}

这是我的ft_substr()

/*
** Function:        char *ft_substr
**
** Description:     Allocates (with malloc(3)) and returns a substring
** from the string ’s’.
** The substring begins at index ’start’ and is of
** maximum size ’len’.
*/
char    *ft_substr(const char *s, unsigned int start, size_t len)
{
unsigned int    i;
unsigned int    j;
char            *str;
i = 0;
j = 0;
if (!s)
return (NULL);
if (start >= ft_strlen(s))
{
if (!(str = (char *)malloc(1)))
return (NULL);
str[0] = '';
return (str);
}
while (s[i] != s[start])
i++;
if (!(str = (char *)malloc((len * sizeof(char)) + 1)))
return (NULL);
while (j < len && s[i])
str[j++] = s[i++];
str[j] = '';
return (str);
}

Answer 1

ft_itoa_base的糟糕设计。return ("0")返回一个指针，指向由两个字符("0"one_answers"\0"(组成的静态分配数组。那个不可能是free-ed。

与lwang <[e-mail]>的此实现进行比较

#include <stdlib.h>
#include <stdio.h>
int     ft_abs(int nb)
{
if (nb < 0)
nb = -nb;
return (nb);
}
char    *ft_itoa_base(int value, int base)
{
char    *str;
int     size;
char    *tab;
int     flag;
int     tmp;
flag = 0;
size = 0;
tab = "0123456789ABCDEF";
if (base < 2 || base > 16)
return (0);
if (value < 0 && base == 10)
flag = 1;
tmp = value;
while (tmp /= base)
size++;
size = size + flag + 1;
str = (char *)malloc(sizeof(char) * size  + 1);
str[size] = '';
if (flag == 1)
str[0] = '-';
while (size > flag)
{
str[size - 1] = tab[ft_abs(value % base)];
size--;
value /=base;
}
return (str);
}