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我是C新手，現在我正在學習mmap。我想從mmaped文件中獲得的第N個字節，但我得到這個錯誤Segmentation Fault (core dumped)當我測試的程序與gdb我得到的東西是不對的線printf("%d\n", (int) data[sk]);然後我print data，我得到從mmaped文件獲得第N個字節
(gdb) print data[sk]
Cannot access memory at address 0xfe5f07d0
(gdb) print data
$1 = 0xfe5f0000 <Address 0xfe5f0000 out of bounds>
我不知道爲什麼我得到這個錯誤。這裏是我的代碼
int main(int argc, char * argv[]){
int sk;
int d;
char *data;
size_t s;
if(argc == 3){
sk = atoi(argv[2]);
d = da_open(argv[1]);
s = da_fileSize(d);
data = (char*)da_mmap(d, s);
printf("File Size: %d\n", (int) s);
printf("%d\n", (int) data[sk]); // this line is bad. But why?
close(d);
}
return 0;
}
而且，這裏是我的全部代碼
#include <stdio.h>
#include <stdlib.h>
#include <sys/mman.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/time.h>
#include <string.h>
int da_open(const char *name);
void *da_mmap(int d, size_t size);
size_t da_fileSize();
int da_open(const char *name){
int dskr;
dskr = open(name, O_RDWR);
if(dskr == -1){
perror(name);
exit(1);
}
printf("dskr1 = %d\n", dskr);
return dskr;
}
void *da_mmap(int d, size_t size){
void *a = NULL;
a = mmap(NULL, size, PROT_WRITE, MAP_SHARED, d, 0);
if(a == MAP_FAILED){
perror("mmap failed");
abort();
}
return a;
}
size_t da_fileSize(int d){
struct stat info;
if(fstat(d, &info) == -1) {
perror("fstat failed");
exit(1);
}
return (size_t)info.st_size;
}
int main(int argc, char * argv[]){
int sk;
int d;
char *data;
size_t s;
if(argc == 3){
sk = atoi(argv[2]);
d = da_open(argv[1]);
s = da_fileSize(d);
data = (char*)da_mmap(d, s);
printf("File Size: %d\n", (int) s);
printf("%d\n", (int) data[sk]);
close(d);
}
return 0;
}