我目前正在学习编程，我正在学习第一年。我们目前正在研究 C，我们的任务是创建一个有点像getline()的函数，但不同之处在于该函数只接受文件描述符作为参数，并在每次调用时返回一个malloc'd字符串，该字符串表示文件中对应于文件描述符的下一行。
函数返回的行不得包含任何''字符，当没有剩余内容要读取或函数遇到错误时，必须返回NULL。我们还仅限于以下功能：读取、malloc 和 free。
我写了以下代码(对不起，如果很难阅读，我还在学习，我们在编写代码时要遵循"编码风格")：
#include "get_next_line.h"
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdio.h>
int find_n(char *str)
{
int i = 0;
while (str[i] != ' ') {
if (str[i] == 'n')
return (i);
i++;
}
return (0);
}
static char *my_realloc(char *str, unsigned int size, unsigned int start_at)
{
int i = 0;
char *new_str;
new_str = malloc(size);
while (str[i + start_at] != ' ') {
new_str[i] = str[i + start_at];
i++;
}
if (str[i + start_at] == ' ')
new_str[i] == ' ';
free(str);
return (new_str);
}
static char *get_line(char *str, unsigned int *total_read)
{
int i = find_n(str);
int j = 0;
int len = 0;
char *line = malloc(i + 1);
while (j < i) {
line[j] = str[j];
j++;
}
line[j] = ' ';
while (str[i + 1 + len] != ' ') {
len++;
}
*total_read = len;
str = my_realloc(str, len + 1, i + 1);
return (line);
}
static void my_strcat(char *dest, char const *src)
{
int dest_len = 0;
int i = 0;
while (dest[i] != ' ') {
i++;
}
dest_len = i;
i = 0;
while (src[i] != ' ') {
dest[dest_len + i] = src[i];
i++;
}
dest[dest_len + i] = ' ';
}
static char *get_text(int fd, char *str)
{
char *buf;
int n_read = READ_SIZE;
static unsigned int total_read = 0;
int loop_started = 0;
buf = malloc(READ_SIZE + 1);
buf[0] = ' ';
while (n_read == READ_SIZE) {
n_read = read(fd, buf, READ_SIZE);
if (n_read == -1 || (n_read == 0 && !loop_started)) {
free(str);
free(buf);
return (NULL);
}
buf[n_read] = ' ';
total_read += n_read;
str = my_realloc(str, total_read + 1, 0);
my_strcat(str, buf);
loop_started = 1;
if (find_n(buf)) {
break;
}
}
free(buf);
return (get_line(str, &total_read));
}
char *get_next_line(int fd)
{
static char *str;
int is_str_malloced = 0;
if (!is_str_malloced) {
str = malloc(1);
str[0] = ' ';
is_str_malloced = 1;
}
return(get_text(fd, str));
}
int main(void)
{
char *str;
int fd;
fd = open("script", O_RDONLY);
while (1) {
str = get_next_line(fd);
if (str == NULL) {
close(fd);
return (0);
}
printf("%sn", str);
}
close(fd);
return (0);
}
主要功能几乎仅用于测试目的。当我编译和测试它时，我得到：
*** Error in `./a.out': free(): invalid next size (normal): 0x0000000000ed71b0 ***
======= Backtrace: =========
/lib64/libc.so.6(+0x7cbac)[0x7f67d51a5bac]
/lib64/libc.so.6(+0x87a59)[0x7f67d51b0a59]
/lib64/libc.so.6(cfree+0x16e)[0x7f67d51b63be]
./a.out[0x40071b]
./a.out[0x40095f]
./a.out[0x400a07]
./a.out[0x400a32]
/lib64/libc.so.6(__libc_start_main+0xea)[0x7f67d514988a]
./a.out[0x40059a]
======= Memory map: ========
00400000-00401000 r-xp 00000000 103:05 22939320 /home/ldidierjean/delivery/CPE_getnextline_2017/a.out
00600000-00601000 r--p 00000000 103:05 22939320 /home/ldidierjean/delivery/CPE_getnextline_2017/a.out
00601000-00602000 rw-p 00001000 103:05 22939320 /home/ldidierjean/delivery/CPE_getnextline_2017/a.out
00ed7000-00ef8000 rw-p 00000000 00:00 0 [heap]
7f67d0000000-7f67d0021000 rw-p 00000000 00:00 0
7f67d0021000-7f67d4000000 ---p 00000000 00:00 0
7f67d4f12000-7f67d4f28000 r-xp 00000000 103:05 7210485 /usr/lib64/libgcc_s-7-20170915.so.1
7f67d4f28000-7f67d5127000 ---p 00016000 103:05 7210485 /usr/lib64/libgcc_s-7-20170915.so.1
7f67d5127000-7f67d5128000 r--p 00015000 103:05 7210485 /usr/lib64/libgcc_s-7-20170915.so.1
7f67d5128000-7f67d5129000 rw-p 00016000 103:05 7210485 /usr/lib64/libgcc_s-7-20170915.so.1
7f67d5129000-7f67d52f4000 r-xp 00000000 103:05 7217643 /usr/lib64/libc-2.25.so
7f67d52f4000-7f67d54f4000 ---p 001cb000 103:05 7217643 /usr/lib64/libc-2.25.so
7f67d54f4000-7f67d54f8000 r--p 001cb000 103:05 7217643 /usr/lib64/libc-2.25.so
7f67d54f8000-7f67d54fa000 rw-p 001cf000 103:05 7217643 /usr/lib64/libc-2.25.so
7f67d54fa000-7f67d54fe000 rw-p 00000000 00:00 0
7f67d54fe000-7f67d5525000 r-xp 00000000 103:05 7219338 /usr/lib64/ld-2.25.so
7f67d56f6000-7f67d56f9000 rw-p 00000000 00:00 0
7f67d5721000-7f67d5724000 rw-p 00000000 00:00 0
7f67d5724000-7f67d5725000 r--p 00026000 103:05 7219338 /usr/lib64/ld-2.25.so
7f67d5725000-7f67d5727000 rw-p 00027000 103:05 7219338 /usr/lib64/ld-2.25.so
7fff51a9b000-7fff51abd000 rw-p 00000000 00:00 0 [stack]
7fff51ac2000-7fff51ac5000 r--p 00000000 00:00 0 [vvar]
7fff51ac5000-7fff51ac7000 r-xp 00000000 00:00 0 [vdso]
ffffffffff600000-ffffffffff601000 r-xp 00000000 00:00 0 [vsyscall]
Abandon (core dumped)
瓦尔格林德给我：
==6142== Memcheck, a memory error detector
==6142== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al.
==6142== Using Valgrind-3.13.0 and LibVEX; rerun with -h for copyright info
==6142== Command: ./a.out --track-origins=yes
==6142==
==6142== Conditional jump or move depends on uninitialised value(s)
==6142== at 0x400824: my_strcat (get_next_line.c:67)
==6142== by 0x400960: get_text (get_next_line.c:98)
==6142== by 0x4009F1: get_next_line (get_next_line.c:118)
==6142== by 0x400A1C: main (get_next_line.c:128)
==6142==
==6142== Invalid read of size 1
==6142== at 0x40081F: my_strcat (get_next_line.c:67)
==6142== by 0x400960: get_text (get_next_line.c:98)
==6142== by 0x4009F1: get_next_line (get_next_line.c:118)
==6142== by 0x400A1C: main (get_next_line.c:128)
==6142== Address 0x5214257 is 0 bytes after a block of size 16,759 alloc'd
==6142== at 0x4C2EB6B: malloc (vg_replace_malloc.c:299)
==6142== by 0x4006B3: my_realloc (get_next_line.c:31)
==6142== by 0x400949: get_text (get_next_line.c:97)
==6142== by 0x4009F1: get_next_line (get_next_line.c:118)
==6142== by 0x400A1C: main (get_next_line.c:128)
==6142==
==6142== Invalid write of size 1
==6142== at 0x400857: my_strcat (get_next_line.c:73)
==6142== by 0x400960: get_text (get_next_line.c:98)
==6142== by 0x4009F1: get_next_line (get_next_line.c:118)
==6142== by 0x400A1C: main (get_next_line.c:128)
==6142== Address 0x5214270 is 16 bytes after a block of size 16,768 in arena "client"
==6142==
==6142== Invalid write of size 1
==6142== at 0x400883: my_strcat (get_next_line.c:76)
==6142== by 0x400960: get_text (get_next_line.c:98)
==6142== by 0x4009F1: get_next_line (get_next_line.c:118)
==6142== by 0x400A1C: main (get_next_line.c:128)
==6142== Address 0x5214277 is 23 bytes after a block of size 16,768 in arena "client"
==6142==
==6142== Conditional jump or move depends on uninitialised value(s)
==6142== at 0x4006F7: my_realloc (get_next_line.c:32)
==6142== by 0x400949: get_text (get_next_line.c:97)
==6142== by 0x4009F1: get_next_line (get_next_line.c:118)
==6142== by 0x400A1C: main (get_next_line.c:128)
==6142==
==6142== Invalid read of size 1
==6142== at 0x4006F2: my_realloc (get_next_line.c:32)
==6142== by 0x400949: get_text (get_next_line.c:97)
==6142== by 0x4009F1: get_next_line (get_next_line.c:118)
==6142== by 0x400A1C: main (get_next_line.c:128)
==6142== Address 0x5214257 is 0 bytes after a block of size 16,759 alloc'd
==6142== at 0x4C2EB6B: malloc (vg_replace_malloc.c:299)
==6142== by 0x4006B3: my_realloc (get_next_line.c:31)
==6142== by 0x400949: get_text (get_next_line.c:97)
==6142== by 0x4009F1: get_next_line (get_next_line.c:118)
==6142== by 0x400A1C: main (get_next_line.c:128)
==6142==
==6142== Invalid read of size 1
==6142== at 0x4006D8: my_realloc (get_next_line.c:33)
==6142== by 0x400949: get_text (get_next_line.c:97)
==6142== by 0x4009F1: get_next_line (get_next_line.c:118)
==6142== by 0x400A1C: main (get_next_line.c:128)
==6142== Address 0x5214257 is 0 bytes after a block of size 16,759 alloc'd
==6142== at 0x4C2EB6B: malloc (vg_replace_malloc.c:299)
==6142== by 0x4006B3: my_realloc (get_next_line.c:31)
==6142== by 0x400949: get_text (get_next_line.c:97)
==6142== by 0x4009F1: get_next_line (get_next_line.c:118)
==6142== by 0x400A1C: main (get_next_line.c:128)
==6142==
==6142== Invalid write of size 1
==6142== at 0x4006DB: my_realloc (get_next_line.c:33)
==6142== by 0x400949: get_text (get_next_line.c:97)
==6142== by 0x4009F1: get_next_line (get_next_line.c:118)
==6142== by 0x400A1C: main (get_next_line.c:128)
==6142== Address 0x521841e is 0 bytes after a block of size 16,766 alloc'd
==6142== at 0x4C2EB6B: malloc (vg_replace_malloc.c:299)
==6142== by 0x4006B3: my_realloc (get_next_line.c:31)
==6142== by 0x400949: get_text (get_next_line.c:97)
==6142== by 0x4009F1: get_next_line (get_next_line.c:118)
==6142== by 0x400A1C: main (get_next_line.c:128)
==6142==
==6142== Invalid read of size 1
==6142== at 0x40070A: my_realloc (get_next_line.c:36)
==6142== by 0x400949: get_text (get_next_line.c:97)
==6142== by 0x4009F1: get_next_line (get_next_line.c:118)
==6142== by 0x400A1C: main (get_next_line.c:128)
==6142== Address 0x5214277 is 23 bytes after a block of size 16,768 in arena "client"
==6142==
--6142-- VALGRIND INTERNAL ERROR: Valgrind received a signal 11 (SIGSEGV) - exiting
--6142-- si_code=1; Faulting address: 0x206991B288; sp: 0x1002ba9e30
valgrind: the 'impossible' happened:
Killed by fatal signal
host stacktrace:
==6142== at 0x5804F2DC: ??? (in /usr/lib64/valgrind/memcheck-amd64-linux)
==6142== by 0x5800B304: ??? (in /usr/lib64/valgrind/memcheck-amd64-linux)
==6142== by 0x5800B4D2: ??? (in /usr/lib64/valgrind/memcheck-amd64-linux)
==6142== by 0x58098653: ??? (in /usr/lib64/valgrind/memcheck-amd64-linux)
==6142== by 0x580A7256: ??? (in /usr/lib64/valgrind/memcheck-amd64-linux)
sched status:
running_tid=1
Thread 1: status = VgTs_Runnable (lwpid 6142)
==6142== at 0x4C2EB6B: malloc (vg_replace_malloc.c:299)
==6142== by 0x4006B3: my_realloc (get_next_line.c:31)
==6142== by 0x400949: get_text (get_next_line.c:97)
==6142== by 0x4009F1: get_next_line (get_next_line.c:118)
==6142== by 0x400A1C: main (get_next_line.c:128)
Note: see also the FAQ in the source distribution.
It contains workarounds to several common problems.
In particular, if Valgrind aborted or crashed after
identifying problems in your program, there's a good chance
that fixing those problems will prevent Valgrind aborting or
crashing, especially if it happened in m_mallocfree.c.
If that doesn't help, please report this bug to: www.valgrind.org
In the bug report, send all the above text, the valgrind
version, and what OS and version you are using. Thanks.
看起来 my_realloc 函数中的 free() 导致程序崩溃，但我根本找不到原因，有人可以帮助我吗？
重建你的realloc是个好主意！
想想你给realloc的start_at价值。
一种更简单的重新分配方法：
char *my_realloc(char *old, int size)
{
int i = 0;
char *new;
new = malloc(sizeof(char) * (my_strlen(old) + size));
while (old[i] != ' ')
{
new[i] = old[i];
i++;
}
free(old);
return (new);
}
另外，我更喜欢这样malloc：
malloc(sizeof(char) * len);
而且这个项目最好有一个get_char：
char get_char(const int fd)
{
static char buff[READ_MAX];
static char* pointer;
static int len = 0;
char caracter;
if (len == 0)
{
len = read(fd, buff, READ_MAX);
pointer = (char*)&buff;
if (len == 0)
return (0);
}
caracter = *pointer;
pointer++;
len--;
return caracter;
}
祝你好运！