无法弄清楚我哪里有内存泄漏

Question

我是 C 的新手，仍然不知道如何使用 valgrind。我正在做一个项目，我需要创建一个函数，该函数 returns 每次仅使用一个静态变量调用时来自文件描述符的一行文本。

Repeated calls (e.g., using a loop) to your get_next_line() function should let you read the text file pointed to by the file descriptor, one line at a time.

我想到了这个，但我找不到内存泄漏的地方：

char    *output(char **backup, char *rbackup, int ret, int fd)
{
    int     value;
    char    *temp;

    if (ret < 0)
        return (NULL);
    else if (ret == 0 && backup[fd] == NULL)
        return (NULL);
    value = (int)(ft_strchr(backup[fd], '\n') - backup[fd] + 1);
    rbackup = ft_substr(backup[fd], 0, value);
    temp = ft_substr(backup[fd], value, BUFFER_SIZE * BUFFER_SIZE);
    free(backup[fd]);
    if (temp[0] == '[=10=]')
    {
        free(temp);
        temp = NULL;
    }
    backup[fd] = temp;
    return (rbackup);
}

char    *get_next_line(int fd)
{
    int         ret;
    char        buf[BUFFER_SIZE + 1];
    static char *backup[NUM_OF_FD];
    char        *rbackup;

    if (fd < 0 || fd > NUM_OF_FD)
        return (NULL);
    while (ft_strchr(backup[fd], '\n') == NULL)
    {
        ret = read(fd, buf, BUFFER_SIZE);
        buf[ret] = '[=10=]';
        if (ret <= 0)
            break ;
        if (backup[fd] == NULL)
            backup[fd] = ft_strdup(buf);
        else
        {
            rbackup = ft_strjoin(backup[fd], buf);
            free(backup[fd]);
            backup[fd] = rbackup;
        }
    }
    return (output(backup, rbackup, ret, fd));
}

ft_函数等同于 LibC 的对应物，但如果有错误，我会 post 它们这里：

void    *ft_memcpy(void *dst, const void *src, size_t n)
{
    size_t  i;

    i = -1;
    if ((dst != src) && n)
        while (++i < n)
            ((unsigned char *)dst)[i] = ((unsigned char *)src)[i];
    return (dst);
}

size_t  ft_strlen(const char *s)
{
    size_t  i;

    i = 0;
    while (s[i])
    {
        i++;
    }
    return (i);
}

char    *ft_strchr(const char *s, int c)
{
    char    chr;

    chr = (char)c;
    if (s == NULL)
        return (NULL);
    while (*s && *s != chr)
        s++;
    if (*s == chr)
        return ((char *)s);
    else
        return (NULL);
}

char    *ft_substr(char const *s, unsigned int start, size_t len)
{
    char    *str;

    if (!s)
        return (NULL);
    if (len > ft_strlen(s))
        len = ft_strlen(s);
    if (start > ft_strlen(s))
        len = 0;
    str = malloc(sizeof(char) * (len + 1));
    if (!str)
        return (NULL);
    str = ft_memcpy(str, &s[start], len);
    str[len] = '[=11=]';
    return (str);
}

char    *ft_strdup(const char *s1)
{
    size_t  len;
    void    *new;

    len = ft_strlen(s1) + 1;
    new = malloc(len);
    if (new == NULL)
        return (NULL);
    return ((char *) ft_memcpy(new, s1, len));
}

char    *ft_strjoin(char const *s1, char const *s2)
{
    int     i;
    char    *str;
    size_t  size;

    if (!s1 || !s2)
        return (NULL);
    i = 0;
    size = (ft_strlen(s1) + ft_strlen(s2) + 1);
    str = malloc(sizeof(char) * size);
    if (!str)
        return (NULL);
    while (*s1)
        str[i++] = *s1++;
    while (*s2)
        str[i++] = *s2++;
    str[i] = '[=11=]';
    return (str);
}

void    *ft_memset(void *b, int c, size_t len)
{
    size_t  i;

    i = -1;
    while (++i < len)
        ((unsigned char *)b)[i] = (unsigned char)c;
    return (b);
}

我的代码有没有菜鸟错误？

Answer 1

好吧，我运行你的代码是这样的

int main(int a, char**b)
{
   int f = open("poop.c", O_RDONLY);
   for(int i = 0; i < 10; i++)
   {
    char *x = get_next_line(f);
    printf("x");
    free(x);
   }
}

阅读前 10 行。 valgrind 没有检测到泄漏（一旦我在循环中添加了 free）

虽然它确实抱怨其他事情

==3695== Invalid read of size 1
==3695==    at 0x109270: ft_memcpy (poop.c:26)
==3695==    by 0x1093BB: ft_substr (poop.c:70)
==3695==    by 0x109619: output (poop.c:120)
==3695==    by 0x109802: get_next_line (poop.c:155)
==3695==    by 0x109857: main (poop.c:162)
==3695==  Address 0x4a4a0a5 is 0 bytes after a block of size 101 alloc'd
==3695==    at 0x483B7F3: malloc (in /usr/lib/x86_64-linux-gnu/valgrind/vgpreload_memcheck-amd64-linux.so)
==3695==    by 0x109408: ft_strdup (poop.c:81)
==3695==    by 0x109724: get_next_line (poop.c:147)
==3695==    by 0x109857: main (poop.c:162)
==3695==
==3695== Conditional jump or move depends on uninitialised value(s)
==3695==    at 0x109546: output (poop.c:114)
==3695==    by 0x109802: get_next_line (poop.c:155)
==3695==    by 0x109857: main (poop.c:162)
==3695==
==3695== Conditional jump or move depends on uninitialised value(s)
==3695==    at 0x109556: output (poop.c:116)
==3695==    by 0x109802: get_next_line (poop.c:155)
==3695==    by 0x109857: main (poop.c:162)
==3695==

好像是读取了一个空行导致的未初始化读取

这里是无效读取

((unsigned char*)dst)[i] = ((unsigned char*)src)[i];

Answer 2

如果您有 C 文件的 Makefile，那么您可以在 Makefile 的标志后添加 -g。如果直接使用clang或gcc编译C文件，可以在clang或gcc后加上-g。然后您可以获得有关您的问题的更多信息。 -g用于调试。如果您不添加它，Valgrind 只会告诉您需要调试的部分（如特定功能）。但是如果你加上-g，你就可以知道你需要调试哪一行了。

Answer 3

你肯定有问题：

static char *backup[NUM_OF_FD];

您检查 fd 是否大于 NUM_OF_FD，但 NUM_OF_FD 仍会尝试在备份数组之外进行索引。

if (fd < 0 || fd > NUM_OF_FD)
        return (NULL);

应该是

if (fd < 0 || fd >= NUM_OF_FD)
        return (NULL);

还要注意 read() 可以 return -1，所以这段代码可能有问题：

ret = read(fd, buf, BUFFER_SIZE);
        buf[ret] = '[=13=]';
        if (ret <= 0)
            break ;

使用前检查 return 值。

无法弄清楚我哪里有内存泄漏

Can't figure out where I have memory leak

c

memory-leaks

valgrind