我创建了一个程序来获取目录中的所有文件，找到各个校验和，然后使用多线程查找总校验和。
我收到了一个分段错误，所以我运行了gdb，看到错误发生在第60行open（）所在的位置。在SO和其他论坛上研究seg故障之后，我尝试实现了一些不同的方法，例如使用FILE *句柄而不是int来更改open（）到fopen（）。事实证明这种改变是错误的。
经过数小时的调试和搜索，我很无能为力，非常感谢任何见解。
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <string.h>
#include <stdarg.h>
#include <fcntl.h>
#include <time.h>
#include <sys/types.h>
#include <dirent.h>
#include <pthread.h> ///Compile with -pthread or -lpthread
#include <sys/stat.h>
#define BUFFER_SIZE (1<<16)
void cleanup();
void get_filenames();
void* get_checksum();
char **filenames;
int file_cnt;
DIR *dir;
//int handle;
FILE *handle;
unsigned int checksum;
unsigned char* ptr;
int length;
int count;
unsigned char* buffer;
int* sum;
unsigned int total = 0;
int main(int argc, char *argv[]){
int i;
pthread_t* file;
atexit(cleanup);
get_filenames();
printf("There are %d files:\n", file_cnt);
file = calloc(sizeof(pthread_t), file_cnt);
sum = calloc(sizeof(int), file_cnt);
for(i=0; i<file_cnt; i++){
printf("%s\n", filenames[i]);
pthread_create(&(file[i]), NULL, get_checksum, (void*)&filenames[i]);
}
for(i=0; i<file_cnt; i++){
total += sum[i];
}
printf("total is: %u\n", total);
return EXIT_SUCCESS;
}
void* get_checksum(void* a){
int b = *((int *)a);
//handle = open(filenames[b], O_RDONLY); //SEG FAULT HERE
handle = fopen(filenames[b], "r"); //SEG FAULT HERE
if( handle == NULL ){
printf( "Can't open file: %s\n", filenames[b]);
exit(1);
}
buffer = malloc(BUFFER_SIZE);
if( buffer == NULL ){
printf( "Can't get enough memory\n" );
exit(1);
}
checksum = 0;
do{
//length = read( handle, buffer, BUFFER_SIZE );
length = read( handle, buffer, (sizeof(char)));
if( length == -1 ){
printf( "Error reading file: %s\n", filenames[b]);
//return NULL;
exit(1);
}
ptr = buffer;
count = length;
while( count-- ){
checksum = checksum + (unsigned int)( *ptr++ );
sum[b] = checksum;
}
} while( length );
printf("Checksum= %d\nTimes at: %d\n", checksum, (int)clock());
}
void cleanup() {
if(filenames && file_cnt > 0) {
while(file_cnt-- > 0) {
if(filenames[file_cnt]) {
free(filenames[file_cnt]);
}
}
free(filenames);
}
if(dir) {
closedir(dir);
}
return;
}
void get_filenames() {
struct dirent *dir_entry;
if((dir = opendir(".")) == NULL) {
fprintf(stderr, "Couldn't open the directory entry for reading\n");
exit(1);
}
errno = 0;
file_cnt = 0;
while((dir_entry = readdir(dir)) != NULL) {
char **new_filenames = filenames;
static int realative_dirs = 0;
if(realative_dirs < 2 &&
(strcmp(".", dir_entry->d_name) == 0 || strcmp("..", dir_entry->d_name) == 0)
) {
realative_dirs++;
continue;
}
new_filenames = (char **)realloc(filenames, sizeof(char **) * (file_cnt + 1));
if(new_filenames == NULL) {
free(filenames[file_cnt]);
fprintf(stderr, "Could not allocate reference for filename[%d]\n", file_cnt);
exit(1);
}
filenames = new_filenames;
filenames[file_cnt] = (char *)calloc(strlen(dir_entry->d_name) + 1, sizeof(char));
if(filenames[file_cnt] == NULL) {
fprintf(stderr, "Could not allocate memory for filename[%d]'s string: \"%s\"\n",
file_cnt, dir_entry->d_name);
exit(1);
}
strcpy(filenames[file_cnt], dir_entry->d_name);
file_cnt++;
}
if(errno != 0) {
fprintf(stderr, "An error occured getting the filenam list\n");
exit(1);
}
return;
}
下面是输出和gdb调试：
There are 24 files:
.windows
.xscreensaver
.alias
.cshrc
Segmentation fault
(gdb) run
Starting program: /home/nolooking/a.out
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib64/libthread_db.so.1".
There are 24 files:
.windows
[New Thread 0x7ffff781e700 (LWP 15957)]
.xscreensaver
[New Thread 0x7ffff701d700 (LWP 15958)]
Program received signal SIGSEGV, Segmentation fault.
[Switching to Thread 0x7ffff781e700 (LWP 15957)]
0x0000000000400d53 in get_checksum (a=0x60b610) at checksum.c:60
60 handle = open(filenames[b], O_RDONLY);
(gdb) backtrace
#0 0x0000000000400d53 in get_checksum (a=0x60b610) at checksum.c:60
#1 0x00007ffff7bc6374 in start_thread () from /lib64/libpthread.so.0
#2 0x00007ffff7907c3d in clone () from /lib64/libc.so.6
(gdb) quit
A debugging session is active.
更新：
我在评论中听取了一位用户的建议，他建议我使用：
handle=fopen((char*)a, "r");。当if语句if(handle==NULL)被注释掉时，我可以成功打印出文件名。当我包含if语句时，我收到以下输出：
There are 24 files:
.windows
.xscreensaver
.alias
.cshrc
Can't open file: p▒`
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <string.h>
#include <stdarg.h>
#include <fcntl.h>
#include <time.h>
#include <sys/types.h>
#include <dirent.h>
#include <pthread.h>
#include <sys/stat.h>
#define BUFFER_SIZE (1<<16)
void cleanup();
void get_filenames();
void* get_checksum();
char **filenames;
int file_cnt;
DIR *dir;
//int handle;
FILE *handle;
unsigned int checksum;
unsigned char* ptr;
int length;
int count;
unsigned char* buffer;
int* sum;
unsigned int total = 0;
int main(int argc, char *argv[]){
int i;
pthread_t* file;
atexit(cleanup);
get_filenames();
printf("There are %d files:\n", file_cnt);
file = calloc(sizeof(pthread_t), file_cnt);
sum = calloc(sizeof(int), file_cnt);
for(i=0; i<file_cnt; i++){
printf("%s\n", filenames[i]);
pthread_create(&(file[i]), NULL, get_checksum, (void*)&filenames[i]);
}
for(i=0; i<file_cnt; i++){
total += sum[i];
}
printf("total is: %u\n", total);
return EXIT_SUCCESS;
}
void* get_checksum(void* a){
int b = *((int *)a);
handle = fopen(((char*)a), "r");
if( handle == NULL ){
printf( "Can't open file: %s\n", ((char*)a));
exit(1);
}
buffer = malloc(BUFFER_SIZE);
if( buffer == NULL ){
printf( "Can't get enough memory\n" );
exit(1);
}
checksum = 0;
do{
length = read( handle, buffer, BUFFER_SIZE );
if( length == -1 ){
printf( "Error reading file: %s\n", ((char*)a));
//return NULL;
exit(1);
}
ptr = buffer;
count = length;
while( count-- ){
checksum = checksum + (unsigned int)( *ptr++ );
//sum[a] = checksum;
}
} while( length );
printf("Checksum= %d\nTimes at: %d\n", checksum, (int)clock());
}
void cleanup() {
if(filenames && file_cnt > 0) {
while(file_cnt-- > 0) {
if(filenames[file_cnt]) {
free(filenames[file_cnt]);
}
}
free(filenames);
}
if(dir) {
closedir(dir);
}
return;
}
void get_filenames() {
struct dirent *dir_entry;
if((dir = opendir(".")) == NULL) {
fprintf(stderr, "Couldn't open the directory entry for reading\n");
exit(1);
}
errno = 0;
file_cnt = 0;
while((dir_entry = readdir(dir)) != NULL) {
char **new_filenames = filenames;
static int realative_dirs = 0;
if(realative_dirs < 2 &&
(strcmp(".", dir_entry->d_name) == 0 || strcmp("..", dir_entry->d_name) == 0)
) {
realative_dirs++;
continue;
}
new_filenames = (char **)realloc(filenames, sizeof(char **) * (file_cnt + 1));
if(new_filenames == NULL) {
free(filenames[file_cnt]);
fprintf(stderr, "Could not allocate reference for filename[%d]\n", file_cnt);
exit(1);
}
filenames = new_filenames;
filenames[file_cnt] = (char *)calloc(strlen(dir_entry->d_name) + 1, sizeof(char));
if(filenames[file_cnt] == NULL) {
fprintf(stderr, "Could not allocate memory for filename[%d]'s string: \"%s\"\n",
file_cnt, dir_entry->d_name);
exit(1);
}
strcpy(filenames[file_cnt], dir_entry->d_name);
file_cnt++;
}
if(errno != 0) {
fprintf(stderr, "An error occured getting the filenam list\n");
exit(1);
}
return;
}
为什么我取消if语句后会收到该输出？
答案 0 :(得分：1)
不要使用＆amp; i 。我稍后会解释一下。您传递给线程的参数是错误的 a 不是整数。它意味着是一个指向字符串的指针......
将线程创建更改为此...
pthread_create(&(file[i]), NULL, get_checksum, filenames[i]);
然后按如下方式打印字符串......
void* get_checksum(void *a){
char *file_name = (char *)a;
printf("filename=%s\n", file_name);
您将字符串作为指向被调用函数的指针传递。在您的代码中，您尝试将其用作数组的索引。
如果你想把索引作为一个整数传递，请注意......这不会起作用..
pthread_create(&(file[i]), NULL, get_checksum, &i);
这是多线程的，＆amp; i 指向的值随循环运行而变化。将指针传递给字符串，在任何情况下都不要在线程运行时更改文件名。
答案 1 :(得分：1)
更改此
pthread_create(&(file[i]), NULL, get_checksum, (void*)&filenames[i]);
是
pthread_create(&(file[i]), NULL, get_checksum, (void*)i);
和这个
int b = *((int *)a);
是
int b = (int)a;
此外，您无法在read()上致电FILE*，因为fopen()会返回fread()。请改用{{1}}。
答案 2 :(得分：-2)
我认为您的问题仅仅是因为您传递的是&filenames[i]，而不仅仅是&i。
然后在void* get_checksum(void* a)中，您尝试将char *用作int。
代码更像是：
for(i=0; i<file_cnt; i++){
printf("%s\n", filenames[i]);
pthread_create(&(file[i]), NULL, get_checksum, (void*)&i);
}
和void* get_checksum(void* a)：
int b = *((int *)a);
handle = fopen(filenames[b], "r");
if( handle == NULL ){
printf( "Can't open file: %s\n", filenames[b]);
exit(1);
}