strncpy()调用引发段错误，请求排查与解决方法

我已经查阅过Stack Overflow上大量相关帖子，但这些帖子里的段错误场景对我都不适用——它们要么是因为给strncpy()的char *dest参数传入了未初始化的内存，要么是传入了错误的size_t num参数。这些帖子普遍建议避免使用strncpy()，但给出的唯一替代方案是strlcpy()。

我的程序目标是找出指定目录中最大的10个文件，输出它们的名称和大小。程序使用静态分配的FS_Info结构体数组存储文件系统条目信息，数组大小固定，当找到比数组中最小条目更大的文件时，会用新条目的值更新那个较小的条目。

原始代码 #

#include <stdio.h>
#include <stdlib.h>
#include <dirent.h>
#include <sys/stat.h>
#include <string.h>
#include <limits.h>
#include <unistd.h>

// size of array used to contain filesystem entries
const size_t fs_info_arr_size = 10;

// A struct to contain the name of a filesystem entry and its size in bytes.
typedef struct FS_Info
{
    char name[PATH_MAX];
    long long size;
} FS_Info;

// global pointer to FS_Info array
FS_Info *fs_info_arr[fs_info_arr_size];

// used to sort fs_entries array descending in terms of entry size
static int compare(const void *a, const void *b)
{
    const struct FS_Info *entryA = (FS_Info *)a;
    const struct FS_Info *entryB = (FS_Info *)b;

    return (entryB->size - entryA->size) - (entryA->size - entryB->size);
}

/*
Iterates over an array of FS_Info structs and returns a pointer to the struct having the smallest size member
*/
FS_Info *get_smallest_entry(FS_Info **entries)
{
    long long smallest = entries[0]->size;
    FS_Info *target;

    for (int i = 1; i < fs_info_arr_size * sizeof(FS_Info); i += sizeof(FS_Info))
    {
        if (entries[i]->size < smallest)
        {
            smallest = entries[i]->size;
            target = entries[i];
        }
    }
    return target;
}

/*
Add entires to the array. If the array is full, use the above function to find the
struct having the smallest file size, and if the current file size is larger, replace it.
*/
void update_fs_info_arr(char *path) // FIXME debug call stack shows that using strncpy here causes segfault
{
    static int items_added = 0;

    struct stat st;
    if (stat(path, &st) == 0)
    {
        if (items_added < fs_info_arr_size) // if array capacity will not be exceeded
        {
            strncpy(fs_info_arr[items_added]->name, path, PATH_MAX);
            // strlcpy(fs_info_arr[items_added]->name, path, sizeof(fs_info_arr[items_added]->name));
            // strncpy(fs_info_arr[items_added]->name, path, sizeof(fs_info_arr[items_added]->name) / sizeof(fs_info_arr[items_added]->name[0]) - 1);
            // fs_info_arr[items_added]->name[sizeof(fs_info_arr[items_added]->name) / sizeof(fs_info_arr[items_added]->name[0]) - 1] = 0;
            fs_info_arr[items_added]->size = st.st_size;

            items_added++;
        }
        else
        // find entry having the smallest size and replace it with the current entry if it is larger
        {
            FS_Info *smallest = get_smallest_entry(fs_info_arr);
            if (st.st_size > smallest->size)
            {
                strncpy(smallest->name, path, PATH_MAX);
                // strlcpy(smallest->name, path, sizeof(smallest->name));
                // strncpy(smallest->name, path, sizeof(smallest->name) / sizeof(smallest->name[0]) - 1);
                // smallest->name[sizeof(smallest->name) / sizeof(smallest->name[0]) - 1] = 0;
                smallest->size = st.st_size;
            }
        }
    }
    else
    {
        printf("Error getting stat for entry %s: %d\n", path, stat(path, &st));
    }
}

void walk(const char *currDir)
{
    DIR *dir = opendir(currDir);
    struct dirent *entry;

    if (dir == NULL)
    {
        printf("%s could not be opened", currDir);
        return;
    }

    while ((entry = readdir(dir)) != NULL)
    {
        // if directory is current dir or parent dir
        if (strcmp(entry->d_name, ".") == 0 || strcmp(entry->d_name, "..") == 0)
        {
            continue;
        }

        char path_to_entry[PATH_MAX];
        snprintf(path_to_entry, sizeof(path_to_entry), "%s/%s", currDir, entry->d_name);
        //snprintf(path_to_entry, sizeof(path_to_entry) - 1, "%s/%s", currDir, entry->d_name);
        //path_to_entry[sizeof(path_to_entry) - 1] = '\0';

        update_fs_info_arr(path_to_entry);

        if (entry->d_type == DT_DIR)
        {
            walk(path_to_entry);
        }
    }
    closedir(dir);
}

int main(int argc, char *argv[])
{

    char target_dir[PATH_MAX];

    strncpy(target_dir, argv[1], PATH_MAX);

    printf("Finding the %zu largest files in: %s\n", fs_info_arr_size, target_dir);

    // recursively visit all entries in the specified directory
    walk(target_dir);

    // sort the entries descending by file size
    qsort(fs_info_arr, fs_info_arr_size, sizeof(*fs_info_arr), compare);

    // output ten largest files found
    for (int i = 0; i < fs_info_arr_size; i++)
    {
        printf("%s\t%lld\n", fs_info_arr[i]->name, fs_info_arr[i]->size);
    }

    return EXIT_SUCCESS;
}

我尝试过参考相关帖子修改strncpy()的size参数，但没有解决问题。

编辑后代码（仍有内存访问错误） #

我根据建议修复了部分逻辑缺陷，但修改后的程序仍然存在内存访问错误：

#include <stdio.h>
#include <stdlib.h>
#include <dirent.h>
#include <sys/stat.h>
#include <string.h>
#include <limits.h>
#include <unistd.h>

// size of array used to contain filesystem entries
const size_t fs_info_arr_size = 10;

/*
    A struct to contain the name of a filesystem entry and its size in bytes.
    An array of this type will be used to catalog all filesystem entries for
    the directory specified as command line argument.
*/
typedef struct FS_Info
{
    char name[PATH_MAX];
    long long size;
} FS_Info;

// global pointer to FS_Info array
FS_Info fs_info_arr[fs_info_arr_size];

// used to sort fs_entries array descending in terms of entry size
static int compare(const void *a, const void *b)
{
    const struct FS_Info *entryA = (FS_Info *)a;
    const struct FS_Info *entryB = (FS_Info *)b;

return entryB->size - entryA->size;
}

/*
Iterates over an array of FS_Info structs and returns a pointer to the struct
having the smallest size member.
*/
FS_Info *get_smallest_entry(FS_Info *entries)
{
    long long smallest = entries[0].size;
    FS_Info *target;

    for (int i = 1; i < fs_info_arr_size; i++)
    {
        if (entries[i].size < smallest)
        {
            smallest = entries[i].size;
            target = &entries[i];
        }
    }
    return target;
}

/*
Add entires to the array. If the array is full, use the above function to find the
struct having the smallest file size, and if the current file size is larger, replace it.
*/
void update_fs_info_arr(char *path) // FIXME debug call stack shows that using strncpy here causes segfault
{
    static int items_added = 0;

    struct stat st;
    if (stat(path, &st) == 0)
    {
        if (items_added < fs_info_arr_size) // if array capacity will not be exceeded
        {
            strncpy(fs_info_arr[items_added].name, path, PATH_MAX);
            fs_info_arr[items_added].size = st.st_size;

            items_added++;
        }
        else
        // find entry having the smallest size and replace it with the current entry if it is larger
        {
            FS_Info *smallest = get_smallest_entry(fs_info_arr);
            if (st.st_size > smallest->size)
            {
                strncpy(smallest->name, path, PATH_MAX);
                smallest->size = st.st_size;
            }
        }
    }
    else
    {
        printf("Error getting stat for entry %s: %d\n", path, stat(path, &st));
    }
}

void walk(const char *currDir)
{
    DIR *dir = opendir(currDir);
    struct dirent *entry;

    if (dir == NULL)
    {
        printf("%s could not be opened", currDir);
        return;
    }

    while ((entry = readdir(dir)) != NULL)
    {
        // if directory is current dir or parent dir
        if (strcmp(entry->d_name, ".") == 0 || strcmp(entry->d_name, "..") == 0)
        {
            continue;
        }

        char path_to_entry[PATH_MAX];
        snprintf(path_to_entry, sizeof(path_to_entry), "%s/%s", currDir, entry->d_name);

        update_fs_info_arr(path_to_entry);

        if (entry->d_type == DT_DIR)
        {
            walk(path_to_entry);
        }
    }
    closedir(dir);
}

int main(int argc, char *argv[])
{

    // a char array to hold a filesystem path
    char target_dir[PATH_MAX];

    strncpy(target_dir, argv[1], PATH_MAX);

    printf("Finding the %zu largest files in: %s\n", fs_info_arr_size, target_dir);

    // recursively visit all entries in the specified directory
    walk(target_dir);

    // sort the entries descending by file size
    qsort(fs_info_arr, fs_info_arr_size, sizeof(*fs_info_arr), compare);

    // output ten largest files found
    for (int i = 0; i < fs_info_arr_size; i++)
    {
        printf("%s\t%lld\n", fs_info_arr[i].name, fs_info_arr[i].size);
    }

    return EXIT_SUCCESS;
}

内容的提问来源于stack exchange，提问作者John Harrington