可能只是 C 新手提出的另一个愚蠢的指针问题。虽然无法弄清楚这一点。似乎我的堆栈框架以某种方式损坏了。作业看起来几乎无关紧要,但它是一个相当基本的 I/O 练习。尝试通过单次读取读取结构数组(不能使用高级 I/O 函数,例如 fread())。
#include "A2_Phase2.h"
void read_directory(Cdir directory[], int cnt)
{
int fd;
char filename[] = "RandomStructDir.bin";
fd = open(filename, O_RDONLY, S_IRWXU);
if (fd < 0)
perror(strcat(filename, " failed to open."));
if (read(fd, &(directory[0].code[0]), sizeof(Cdir) * cnt) < 0) {
perror(strcat(filename, " could not be accessed."));
}
close(fd);
}
int binary_search(Cdir directory[], char *key, int l, int r) {
int mid = (int) r / 2;
if (strncmp(key, directory[mid].code, 3) < 0)
return binary_search(directory, key, l, mid - 1);
else if (strncmp(key, directory[mid].code, 3) > 0)
return binary_search(directory, key, mid + 1, r);
else
return mid;
}
int main(int argc, char *argv[])
{
int COUNTRY_COUNT = atoi(argv[1]);
printf("%d", COUNTRY_COUNT);
Cdir *directory = (Cdir *) malloc(sizeof(Cdir) * COUNTRY_COUNT);
read_directory(directory, COUNTRY_COUNT);
binary_search(directory, "ZWE", 0, 238);
free(directory);
}
我通过 GDB 收到此错误:
Program received signal SIGSEGV, Segmentation fault.
0x0000000000400940 in binary_search (
directory=<error reading variable: Cannot access memory at address 0x7fffff7feff8>,
key=<error reading variable: Cannot access memory at address 0x7fffff7feff0>, l=<error reading variable: Cannot access memory at address 0x7fffff7fefec>,
r=<error reading variable: Cannot access memory at address 0x7fffff7fefe8>)
at A2_Phase2.c:19
19 int binary_search(Cdir directory[], char *key, int l, int r) {
谢谢!
最佳答案
int COUNTRY_COUNT = atoi(argv[1]);
读取国家的数量作为程序的参数,但稍后您在调用时硬编码假设这是 >= 238
binary_search(directory, "ZWE", 0, 238);
你能试试吗
binary_search(directory, "ZWE", 0, COUNTRY_COUNT-1);
相反?您的 binary_search
函数中也有一些错误,可以重写为
int binary_search(Cdir directory[], const char *key, int l, int r)
{
int mid = (r + l) / 2;
int cmp = strncmp(key, directory[mid].code, 3);
if (l >= r) {
if (cmp == 0)
return l;
return -1;
}
if (cmp < 0)
return binary_search(directory, key, l, mid - 1);
else if (cmp > 0)
return binary_search(directory, key, mid + 1, r);
else
return mid;
}
主要变化是
mid
的计算考虑了l
以及r
- (正如 Kirilenko 所指出的)认识到可能找不到匹配项。在这种情况下返回 -1
- 减少调用
strcmp
的次数。非常小,但它使代码对我来说更清晰,并将提高搜索性能
次要的是,有一些风格问题使您的代码难以阅读
- 函数内大量不必要的空格
- 对变量使用大写字母(例如
COUNTRY_COUNT
)是不常见的。所有大写通常非正式地保留给使用小写或驼峰式命名的变量定义
关于c - 读取变量时出错,无法访问地址 X 的内存,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/14484682/