我在malloc/free遇到了问题。我想实现一个简单的'ls'来显示dir中的未隐藏文件。
这是我的代码：
void do_ls(char *dirname, _Bool ls_list) {
DIR *dir_ptr;
const char * d_name;
struct dirent *direntp, ** dirarray;
int fcnt, d_name_max;
if((dir_ptr = opendir(dirname))==NULL) {
fprintf(stderr,"ls: cannot open %s\n", dirname);
exit(-1);
}
else {
fcnt = 0; // count unhidden files
d_name_max = -1; // max length of filename
while((direntp = readdir(dir_ptr))!=NULL) {
d_name = direntp->d_name;
if(d_name[0]!='.' ||\
strcmp(d_name, ".")==0 ||\
strcmp(d_name, "..")==0) {
fcnt++;
if((int)strlen(d_name)>d_name_max)
d_name_max = strlen(d_name);
}
}
// use a array to store dirent printer
dirarray = (struct dirent**)malloc(sizeof(struct dirent *)*fcnt);
// reset read position
seekdir(dir_ptr, 0);
int i = 0;
while((direntp=readdir(dir_ptr))!=NULL) {
if(d_name[0]!='.' ||\
strcmp(d_name, ".")==0 ||\
strcmp(d_name, "..")==0) {
dirarray[i++] = direntp; // save pointer
}
}
qsort(dirarray, fcnt, sizeof(struct dirent*), alphacmp); // qsort for lexicographical ordering
for(int i=0;i<fcnt;i++)
fprintf(stdout, "%s\n", dirarray[i]->d_name); // print result
if(dirarray!=NULL)
free(dirarray); // free if not NULL
closedir(dir_ptr);
}
}
这对我来说很困惑，在某些情况下会起作用或崩溃。我想在do_ls中肯定会有一些错误，但仍然无法找到。
我的目录下的文件是：
`ls -a ~/file/c/`
./ ../ 1* a.c db/ mpi/ test1.c .test1.c.swo .test1.c.swp unix/ .ycm_extra_conf.py .ycm_extra_conf.pyc
但是当运行./my-own-ls ~/file/c/时，我遇到了这些错误：
/home/panhzh3/file/c:
..
.test1.c.swo
.test1.c.swp
.ycm_extra_conf.py
.ycm_extra_conf.pyc
1
mpi
unix
*** glibc detected *** ./ls: free(): invalid next size (fast): 0x08d9b028 ***
======= Backtrace: =========
/lib/i386-linux-gnu/libc.so.6(+0x75b12)[0xb7664b12]
./ls[0x80488e5]
./ls[0x8048a6f]
/lib/i386-linux-gnu/libc.so.6(__libc_start_main+0xf3)[0xb76084d3]
./ls[0x8048621]
======= Memory map: ========
08048000-08049000 r-xp 00000000 08:0a 1183201 /home/panhzh3/file/c/unix/hw/ls
08049000-0804a000 r--p 00000000 08:0a 1183201 /home/panhzh3/file/c/unix/hw/ls
0804a000-0804b000 rw-p 00001000 08:0a 1183201 /home/panhzh3/file/c/unix/hw/ls
08d93000-08dbc000 rw-p 00000000 00:00 0 [heap]
b75b4000-b75d0000 r-xp 00000000 08:09 392702 /lib/i386-linux-gnu/libgcc_s.so.1
b75d0000-b75d1000 r--p 0001b000 08:09 392702 /lib/i386-linux-gnu/libgcc_s.so.1
b75d1000-b75d2000 rw-p 0001c000 08:09 392702 /lib/i386-linux-gnu/libgcc_s.so.1
b75ee000-b75ef000 rw-p 00000000 00:00 0
b75ef000-b7793000 r-xp 00000000 08:09 392617 /lib/i386-linux-gnu/libc-2.15.so
b7793000-b7795000 r--p 001a4000 08:09 392617 /lib/i386-linux-gnu/libc-2.15.so
b7795000-b7796000 rw-p 001a6000 08:09 392617 /lib/i386-linux-gnu/libc-2.15.so
b7796000-b7799000 rw-p 00000000 00:00 0
b77b3000-b77b7000 rw-p 00000000 00:00 0
b77b7000-b77b8000 r-xp 00000000 00:00 0 [vdso]
b77b8000-b77d8000 r-xp 00000000 08:09 392601 /lib/i386-linux-gnu/ld-2.15.so
b77d8000-b77d9000 r--p 0001f000 08:09 392601 /lib/i386-linux-gnu/ld-2.15.so
b77d9000-b77da000 rw-p 00020000 08:09 392601 /lib/i386-linux-gnu/ld-2.15.so
bff21000-bff43000 rw-p 00000000 00:00 0 [stack]
[2] 32254 abort (core dumped) ./ls ~/file/c
源代码：
#include <stdio.h>
#include <sys/types.h>
#include <dirent.h>
#include <unistd.h>
#include <getopt.h>
#include <stdlib.h>
#include <stdbool.h>
#include <string.h>
#include <sys/types.h>
int alphacmp(const void * a, const void * b) {
struct dirent ** ta = (struct dirent**)a;
struct dirent ** tb = (struct dirent**)b;
return strcmp((*ta)->d_name, (*tb)->d_name);
}
void do_ls(char *dirname, _Bool ls_list) {
DIR *dir_ptr;
const char * d_name;
struct dirent *direntp, ** dirarray;
int fcnt, d_name_max;
if((dir_ptr = opendir(dirname))==NULL) {
fprintf(stderr,"ls2: cannot open %s\n", dirname);
exit(-1);
}
else {
fcnt = 0;
d_name_max = -1;
while((direntp = readdir(dir_ptr))!=NULL) {
d_name = direntp->d_name;
if(d_name[0]!='.' ||\
strcmp(d_name, ".")==0 ||\
strcmp(d_name, "..")==0) {
fcnt++;
if((int)strlen(d_name)>d_name_max)
d_name_max = strlen(d_name);
}
}
dirarray = (struct dirent**)malloc(sizeof(struct dirent *)*fcnt);
seekdir(dir_ptr, 0);
int i = 0;
while((direntp=readdir(dir_ptr))!=NULL) {
if(d_name[0]!='.' ||\
strcmp(d_name, ".")==0 ||\
strcmp(d_name, "..")==0) {
dirarray[i++] = direntp;
}
}
qsort(dirarray, fcnt, sizeof(struct dirent*), alphacmp);
for(int i=0;i<fcnt;i++)
fprintf(stdout, "%s\n", dirarray[i]->d_name);
if(dirarray!=NULL)
free(dirarray);
closedir(dir_ptr);
}
}
int main(int argc, char **argv) {
const char * const short_options = "l";
const struct option long_options[] = {
{"list", 0, NULL, 'l'},
{NULL, 0, NULL, 0},
};
const char * program_name = argv[0];
opterr = 0;
int next_option;
_Bool ls_list = false;
do {
next_option = getopt_long(argc, argv, short_options, long_options, NULL);
switch(next_option) {
case 'l':
ls_list = true;
break;
case '?':
fprintf(stderr, "Invalid option: -%c", optopt);
exit(-1);
break;
case ':':
fprintf(stderr, "Option -%c needs argument.", optopt);
case -1:
break;
default:
abort();
}
} while(next_option!=-1);
if(optind == argc)
do_ls(".", ls_list);
else
for(;optind<argc;optind++) {
printf("%s:\n", argv[optind]);
do_ls(argv[optind], ls_list);
}
return 0;
}
答案 0 :(得分：1)
在你的第二个while循环中，你错过了这一行：
d_name = direntp->d_name;
您可能需要知道的另一件事是，您不能依赖于将dirent指针存储在数组中并对它们进行排序。 readdir的手册页说明后续调用可能会覆盖数据，因此您可能需要复制每个条目并对副本进行排序。