如何为char数组动态分配和释放内存？
我的malloc下面不起作用。抛出的错误是预期的＆＃39 ;;＆＃39;在声明清单的末尾。＆＃39;
char *string_buffer = malloc(128 * sizeof(char));
以下是我尝试释放string_buffer [128]字符数组：
void rmv(struct tree_node *cwd) {
struct list_node *child = cwd -> first_child;
free(string = child -> tree -> string_buffer);
printf("String memory free successful\n");
//free(cwd -> first_child -> tree);
//free(cwd -> first_child);
}
其余代码：
Shell命令：
cd =当前目录
ls = list
mkdir = make目录
rmdir =删除目录（未实现 - 需要释放内存）
#include <stdio.h> /* For fgets(), fprintf() and printf() */
#include <stdlib.h> /* For EXIT_FAILURE */
#include <ctype.h> /* For isspace() */
#include <string.h>
#include <stddef.h>
// COMMANDS
char exitProgram[] = "exit";
char listDirectory[] = "ls";
char commandDirectory[] = "cd";
char makeDirectory[] = "mkdir";
char removeDirectory[] = "rmdir";
// holds a string buffer of length 128
// a pointer to its parent
// a pointer to the first node of the list of children
typedef struct tree_node {
char string_buffer[128];
struct tree_node *parent;
struct list_node *first_child; // first node of list of children?
} tree_node;
// pointer to tree node
// pointer to next item in the list
typedef struct list_node {
struct tree_node *tree;
struct list_node *next;
} list_node;
// allocates the right amount of space for a tree node
// sets the pointers to NULL
// initialises the string buffer with the given name
// returns a pointer to the tree node
struct tree_node *make_tree_node(char *name) {
tree_node *instance = malloc(sizeof(*instance));
instance -> parent = NULL;
instance -> first_child = NULL;
strcpy(instance -> string_buffer, name);
return instance;
}
// allocates a new list node
// assigns the fields for the tree node it references and the next list node
// returns a pointer to the new list node
struct list_node *make_list_node(struct tree_node *v, struct list_node *next) {
list_node *instance = malloc(sizeof(*instance));
instance -> tree = v;
instance -> next = next;
return instance;
}
// checks whether directory named arg already exists in current working directory
// creates the directory if it does not exist
// if arg is NULL, the function should print an error message
void do_mkdir(struct tree_node *cwd, char *arg) {
//printf("Making Directory with name %s\n", arg);
if (NULL == arg || !strcmp(arg, "")) {
printf("Please specify directory name that is not NULL: mkdir directoryName\n");
}
else {
// check if directory exists
struct list_node *subDir = cwd->first_child;
while (subDir != NULL) {
if (strcmp(subDir -> tree -> string_buffer, arg) == 0) {
printf("Directory with that name exists. Please provide another name.\n");
return;
}
subDir = subDir -> next;
}
// adding new directory
struct tree_node *newSubDir = make_tree_node(arg);
newSubDir -> parent = cwd;
struct list_node *newListNode = make_list_node(newSubDir, NULL);
// putting new node in alphabetical order
struct list_node *prev = NULL;
if (subDir == NULL) {
newListNode -> next = cwd -> first_child;
cwd -> first_child = newListNode;
} else {
while (subDir != NULL) {
// TODO: use case insensitive compare
if (strcmp(arg, subDir -> tree -> string_buffer) > 0) {
// inserting in front
newListNode -> next = subDir -> next;
prev->next = newListNode;
break;
}
prev = subDir;
subDir = subDir -> next;
}
if (subDir == NULL) {
subDir->next = newListNode;
}
}
}
}
// prints all children of the directory cwd (not recursively)
void do_ls(struct tree_node *cwd) {
printf("Listing Directories...\n");
struct list_node *subDir = cwd -> first_child;
while (subDir != NULL) {
printf("%s\n", subDir ->tree -> string_buffer);
subDir = subDir->next;
}
}
// *checks whether cwd has a subdirectory named arg
// *if yes, the function returns the corresponding tree node (and become new working directory)
// *if no, prints an error message
// *handle cd and cd ..
struct tree_node *do_cd(struct tree_node *cwd, struct tree_node *root, char *arg) {
// initialising subDir to cwd's first child
struct list_node *subDir = cwd -> first_child;
// initialising parDir to cwd's parent
struct tree_node *parDir = cwd -> parent;
if (parDir != NULL) { // root directory does not have a parent directory
if (strcmp(arg, "..") == 0) {
cwd = parDir;
printf("Returning to parent directory.\n");
return cwd;
}
}
// checks if user input argument is "."
if (strcmp(arg, ".") == 0) {
return cwd;
}
// checks if user input argument is NULL or ""
if (NULL == arg || !strcmp(arg, "")) {
printf("Returning to root directory.\n");
return root;
}
// checks if cwd has a subdirectory named arg
while (subDir != NULL) {
if (strcmp(subDir -> tree -> string_buffer, arg) == 0) {
printf("Subdirectory exists!\n");
cwd = subDir-> tree;
printf("Making & entering subdirectory: %s\n", arg);
return cwd;
}
subDir = subDir-> next;
}
printf("Directory does not exist!\n");
return cwd;
}
// *prints the prompt (e.g. /bar/baz/ >) in every iteration of the main loop
// *show all directories on the path in correct order
void show_prompt(struct tree_node *cwd) {
struct tree_node *originalDir = cwd;
if (cwd -> parent != NULL) {
show_prompt(cwd -> parent);
printf("/%s", cwd -> string_buffer);
}
cwd = originalDir;
}
// *removes a node child from its parent node dir
// *take care to correctly support corner cases like the child being the only one
// *all memory occupied by the child should be freed
void remove_child(struct tree_node *cwd, struct tree_node *child) {
child = cwd -> first_child -> tree;
cwd = child -> parent;
if (cwd -> first_child -> tree == NULL) {
printf("Subdirectory is not empty!\n");
}
else if (cwd -> first_child != NULL) {
free(child);
}
}
void rmv(struct tree_node *cwd) {
struct list_node *child = cwd -> first_child;
printf("%s\n", child -> tree -> string_buffer);
strcpy(child -> tree -> string_buffer, "");
printf("String memory free successful\n");
free(child -> tree -> string_buffer);
//free(cwd -> first_child -> tree);
//free(cwd -> first_child);
}
void rmv2(struct tree_node *cwd) {
struct tree_node *child = cwd -> first_child -> tree;
free(child);
}
void rmv3(struct tree_node *cwd) {
struct tree_node *child = cwd -> first_child -> tree;
cwd = child -> parent;
if (strcmp(cwd -> first_child -> tree -> string_buffer, "\0") == 0) {
printf("Subdirectory is not empty!\n");
}
else if (cwd -> first_child != NULL) {
free(cwd -> first_child -> tree -> string_buffer);
free(cwd -> first_child -> tree);
free(cwd -> first_child);
}
}
// implement rmdir (follow same pattern as previous exercise)
// *if the specified directory is not empty, rmdir should fail with an error message
void do_rmdir(struct tree_node *cwd, char *arg) {
struct list_node *subDir = cwd->first_child;
// checks if user input argument is NULL or ""
if (NULL == arg || !strcmp(arg, "")) {
printf("Please specify a directory that is not NULL: rmdir directoryName.\n");
}
while(subDir != NULL) {
if (strcmp(subDir -> tree -> string_buffer, arg) != 0) {
printf("Directory does not exist!\n");
}
subDir = subDir -> next;
}
if (strcmp(subDir -> tree -> string_buffer, arg) == 0) {
if (subDir -> tree == NULL) {
free(subDir);
}
while (subDir != NULL) {
if (strcmp(subDir -> tree -> string_buffer, arg) == 0) {
printf("Directory with that name exists. Please provide another name.\n");
return;
}
subDir = subDir -> next;
}
} else {
printf("Directory does not exist!\n");
}
}
int main(void) {
char directoryName[129] = "";
printf("\nProgram Start... \n\n");
// getting user input string
// and capturing argument from user input
char inputString[129];
char delimiter[] = " ";
char *line;
char *arg;
struct tree_node *root = make_tree_node("root\0");
struct tree_node *cwd = root;
printf("/ >");
while (fgets(inputString, 128, stdin)) {
inputString[strlen(inputString) - 1] = '\0';
// gets argument and stores as arg
line = malloc(strlen(inputString) + 1);
strcpy(line, inputString);
arg = strsep(&line, delimiter);
arg = strsep(&line, delimiter);
//printf("your argument: %s\n", arg);
if(strncmp(inputString, "exit", 4) == 0) {
printf("Breaking...\n");
break;
}
//////////////////////////////// HANDLING LS ////////////////////////////
else if(strncmp(inputString, "ls ", 3) == 0) {
printf("The ls command should be used without arguments.\n");
}
else if(strncmp(inputString, "ls", 2) == 0) {
do_ls(cwd);
show_prompt(cwd);
printf("/ >");
}
/////////////////////////// HANDING CD (EXTRA SAFE) //////////////////////////////
else if(strncmp(inputString, "cd ..", 5) == 0) {
cwd = do_cd(cwd, root, arg);
show_prompt(cwd);
printf("/ >");
}
else if(strncmp(inputString, "cd .", 4) == 0) {
cwd = do_cd(cwd, root, arg);
show_prompt(cwd);
printf("/ >");
}
else if(strncmp(inputString, "cd ", 3) == 0) {
cwd = do_cd(cwd, root, arg);
show_prompt(cwd);
printf("/ >");
}
else if(strncmp(inputString, "cd", 2) == 0) {
cwd = root;
printf("Returning to root directory.\n");
show_prompt(cwd);
printf("/ >");
}
////////////////////////////// HANDLING MKDIR /////////////////////////////////////
else if(strncmp(inputString, "mkdir ", 7) == 0) {
printf("Please specify directory name that is not NULL: mkdir directoryName\n");
show_prompt(cwd);
printf("/ >");
}
else if(strncmp(inputString, "mkdir ", 6) == 0) {
do_mkdir(cwd, arg);
show_prompt(cwd);
printf("/ >");
}
else if(strncmp(inputString, "mkdir", 5) == 0) {
printf("Please specify directory name: mkdir directoryName\n");
show_prompt(cwd);
printf("/ >");
}
////////////////////////////// HANDLING RMDIR /////////////////////////////////////
else if(strncmp(inputString, "rmdir ", 7) == 0) {
printf("Please specify directory name that is not NULL: rmdir directoryName\n");
show_prompt(cwd);
printf("/ >");
}
else if(strncmp(inputString, "rmdir ", 6) == 0) {
printf("Removing Directory with name...\n");
do_rmdir(cwd, arg);
show_prompt(cwd);
printf("/ >");
}
else if(strncmp(inputString, "rmv", 3) == 0) {
printf("Removing first child test\n");
struct tree_node *child = cwd -> first_child -> tree;
rmv(cwd);
show_prompt(cwd);
printf("/ >");
}
else if(strncmp(inputString, "rmdir", 5) == 0) {
printf("Please specify directory name: rmdir directoryName\n");
show_prompt(cwd);
printf("/ >");
}
else {
printf("Unrecognised input: Please try again.\n");
show_prompt(cwd);
printf("/ >");
}
}
printf("\nProgram Quit... \n\n");
return 0;
}
答案 0 :(得分：0)
For the compiler to issue such a diagnostic, you must be trying to define a global variable with a non-constant initializer:
public ObservableCollection<Attachment> AttachmentLst
{
get { return _attachmentLst; }
set { SetProperty(ref _attachmentLst, value); }
}
#endregion
#region Commands
public ICommand AttachmentChecked
{
get
{
return _attachmentChecked ?? (_attachmentChecked = new CommandHandlerWithParam(obj => ExecuteAttachmentChecked(obj), CanExecuteAttachmentChecked()));
}
}
private void ExecuteAttachmentChecked(object obj)
{
}
private bool CanExecuteAttachmentChecked()
{
return true;
}This cannot be done at the global level.
You must define char *string_buffer = malloc(128 * sizeof(char));
with a constant initializer such as string_buffer, or no initializer at all, which will have the same effect, and allocate the memory at startup, in the NULL function:
main()Note that if you do not need to reallocate char *string_buffer;
int main(void) {
string_buffer = malloc(128);
...
}
during the course of the program, you do not need to make it a pointer to dynamic memory, just defining a global array should suffice:
string_buffer