我过去做过类似的事情，所以我不确定为什么当我尝试将我的指针打印到一个指针数组时，我得到一堆 (null) 作为输出。这是我在文件底部附近所说的代码:
int z = 0;
while (z < 9) {
printf("%s ", allLines[z]->username);
z++;
}
我想做的是从用户那里获取一个目录(相对或绝对)，然后切换到该目录并打开该目录中的所有文本文件，以便我可以从中提取每一行并存储每一行在记录结构中。请在下面查看我的代码:
#define _GNU_SOURCE
#define MAXLINE 256
#define MAXPATHLENGTH 1024
#define MAXRECORDS 10000
#include <fcntl.h>
#include <unistd.h>
#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <dirent.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <pthread.h>
typedef struct records {
char* username;
char* password;
char* bloodType;
char* domainName;
char* index;
} records;
int main(int argc, char** argv) {
if(argc != 2) {
printf("You must provide 2 arguments: <./filename> <directory>\n");
return -1;
}
char* path = malloc(MAXPATHLENGTH * sizeof(char));
char* cwd = malloc(MAXPATHLENGTH * sizeof(char));
FILE* sortedFile;
FILE* dirEntry;
DIR* dirp; //pointer to a directory stream
struct dirent* dirstructp; //pointer to a dirent structure
struct stat buffer;
records** allLines = malloc(MAXRECORDS * sizeof(records));
int linesInFile[MAXRECORDS];
records** files = calloc(MAXRECORDS, sizeof(records)); //pointer to an array of pointers (each of which point to a records struct)
int totalFiles;
if ((sortedFile = fopen("sorted.yay", "w+")) == NULL) {
fprintf(stderr, "%s\n", strerror(errno));
printf("fopen");
exit(errno);
}
//changes the current working directory of the calling process to the directory specified
if((chdir(argv[1])) == -1) {
fprintf(stderr, "%s\n", strerror(errno));
exit(errno);
}
/*copies the pathname of the current working directory to the array pointed to by cwd, which is of length MAXPATHLENGTH*/
if((path = getcwd(cwd, MAXPATHLENGTH)) == NULL) {
fprintf(stderr, "%s\n", strerror(errno));
exit(errno);
}
//returns a pointer to the directory stream if successful
if((dirp = opendir(path)) == NULL) {
fprintf(stderr, "%s\n", strerror(errno));
printf("opendir");
exit(errno);
}
int i = 0;
int j = 0;
int l = 0;
while((dirstructp = readdir(dirp)) != NULL) {
if ((strncmp(dirstructp->d_name, ".", strlen(".")) != 0) && (strncmp(dirstructp->d_name, "..", strlen("..")) != 0)) {
if(lstat(dirstructp->d_name, &buffer) == -1) {
fprintf(stderr, "%s\n", strerror(errno));
printf("Bob Saget");
exit(errno);
}
if(S_ISREG(buffer.st_mode)) {
if ((dirEntry = fopen(dirstructp->d_name, "r")) == NULL) {
fprintf(stderr, "%s\n", strerror(errno));
printf("fopen2");
exit(errno);
}
char* buf = malloc(MAXLINE * sizeof(char));
while(fgets(buf, MAXLINE, dirEntry)) {
records* line = malloc(sizeof(records));
int k = 0;
while(k < 5) {
char* token = malloc(MAXLINE * sizeof(char));
token = strsep(&buf,",");
switch(k) {
case 0:
line->username = malloc(MAXLINE * sizeof(char));
strncpy(line->username, token, strlen(token));
break;
case 1:
line->password = malloc(MAXLINE * sizeof(char));
strncpy(line->password, token, strlen(token));
break;
case 2:
line->bloodType = malloc(MAXLINE * sizeof(char));
strncpy(line->bloodType, token, strlen(token));
break;
case 3:
line->domainName = malloc(MAXLINE * sizeof(char));
strncpy(line->domainName, token, strlen(token));
break;
case 4:
line->index = malloc(MAXLINE * sizeof(char));
strncpy(line->index, token, strlen(token));
break;
}
k++;
}
allLines[l] = line;
l++;
free(line);
free(buf);
buf = malloc(MAXLINE * sizeof(char));
}
linesInFile[j] = i;
i = 0;
files[j] = allLines;
j++;
totalFiles = j;
free(buf);
}
}
}
int z = 0;
while (z < 9) {
printf("%s ", allLines[z]->username);
z++;
}
return 0;
}
最佳答案
records* line = malloc(sizeof(records));
...
line->username = malloc(MAXLINE * sizeof(char));
...
allLines[l] = line;
...
free(line);
...
printf("%s ", allLines[z]->username);
您释放了 allLines[z]指针，因此它无效并且访问它是未定义的行为。
- 我建议您清理代码。
- 另外，下次请发一个 MCVE这是重现问题所需的最小示例。
- 这是学习如何调试程序的好时机。
-
char* token = malloc(MAXLINE * sizeof(char));<br/> token = strsep(&buf,",");只是泄漏内存.... - 如果行格式不正确并且
token = strsep(&buf,",");怎么办？返回 NULL？您的代码将在strncpy(line->index, token, strlen(token));中执行未定义的行为并且该程序很可能会在 Linux 上收到 sigsegv。 -
char* buf = malloc(MAXLINE * sizeof(char)); while(fgets(buf, MAXLINE, dirEntry)) {和free(buf);<br/> buf = malloc(MAXLINE * sizeof(char));.具有相同缓冲区的 free + malloc 毫无意义。 - 请正确缩进您的代码。如果您的代码有超过 3 个级别的标识，那么是时候创建一个函数了。好好读一读:Linux kernel coding style .
- 所有
strncpy(line->password, token, strlen(token));只是奇怪。首先，它与strcpy(line->password, token)相同第二个如果strlen(token)等于 MAXLINE 输出将不会以 null 终止，其次如果strlen(token)大于 MAXLINE 这将调用未定义的行为。你应该line->username = malloc((strlen(token) + 1) * sizeof(char)); memcpy(line->username, token, strlen(token) + 1);或者只是line->username = strdup(token);.对if (line->username == NULL) { handle errors; }也很好.或者使用简单的if (strlen(token) >= MAXLINE) { fprintf(stderr, "token too long!"); abort(); }来防止 UB .或者你可以strlcpy(line->username, token, MAXLINE)这将防止溢出并始终以 null 终止输出。不要使用strncpy，这是一个糟糕的功能。 allLines的分配是无效的。records** allLines = malloc(MAXRECORDS * sizeof(records));它应该分配一个sizeof(records*)的数组指针不是记录。您可以分配一个数组records* allLines = malloc(MAXRECORDS * sizeof(records));这可能可以用allLines[l] = *line;修复你的代码.但是访问需要使用.然后->, 比如printf需要用printf("%s ", allLines[z].username);更改- 同样适用于
records** files = calloc(MAXRECORDS, sizeof(records));这是指向文件指针的指针。 - 可移植且位置正确定义的宏，其含义可能与
MAXPATHLENGTH相同是PATH_MAX在limits.h中定义 -
char* path = malloc(MAXPATHLENGTH * sizeof(char));和path = getcwd(cwd, MAXPATHLENGTH)泄漏内存(!)而且很奇怪。成功path == cmd...我建议你只想要cmd = get_current_dir_name().
关于c - 为什么我不能将指向结构的指针保存为指向指针数组的指针的索引？，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/53403384/