求助C++下面这几句malloc到底应该怎么写才能通过VC 6的编译？

[「已注销」]

9 #define xmalloc malloc //这句的应该是说xmalloc和malloc是一样的吧
44 ret = xmalloc(sizeof(struct path));
117 file = xmalloc(sizeof(struct file));
154 handle = xmalloc(sizeof(struct dir));
169 handle = xmalloc(sizeof(struct dir));
186 entry = xmalloc(sizeof(struct direntry));

出错代码如下
--------------------Configuration: fs - Win32 Debug--------------------
Compiling...
filesystem.cpp
c:\复件 fs_dumper\filesystem.cpp(44) : error C2440: '=' : cannot convert from 'void *' to 'struct path *'
Conversion from 'void*' to pointer to non-'void' requires an explicit cast
c:\复件 fs_dumper\filesystem.cpp(117) : error C2440: '=' : cannot convert from 'void *' to 'struct file *'
Conversion from 'void*' to pointer to non-'void' requires an explicit cast
c:\复件 fs_dumper\filesystem.cpp(134) : warning C4018: '>' : signed/unsigned mismatch
c:\复件 fs_dumper\filesystem.cpp(154) : error C2440: '=' : cannot convert from 'void *' to 'struct dir *'
Conversion from 'void*' to pointer to non-'void' requires an explicit cast
c:\复件 fs_dumper\filesystem.cpp(169) : error C2440: '=' : cannot convert from 'void *' to 'struct dir *'
Conversion from 'void*' to pointer to non-'void' requires an explicit cast
c:\复件 fs_dumper\filesystem.cpp(186) : error C2440: '=' : cannot convert from 'void *' to 'struct direntry *'
Conversion from 'void*' to pointer to non-'void' requires an explicit cast
执行 cl.exe 时出错.

fs.exe - 1 error(s), 0 warning(s)
源文件在这下载http://www.mediafire.com/?h1nhf53b165te6o
其中的filesystem.cpp在下面

#include <stdio.h>
#include <cstdlib>
#include <string.h>
#include <winsock2.h>
#include "nand.h"
#include "filesystem.h"

#define xmalloc malloc

#define MIN(a,b) ((a)>(b)?(b):(a))

static FILE * rom_fh;
static unsigned long start_blk;

unsigned long find_fs(FILE * fh)
{
	struct nand_block blk = {0,};
	unsigned long blkno = 0;
	while(1) {
		if (!read_nand(fh, blkno, &blk)) {
			blkno = 0;
			break;
		}
		if (memcmp(blk.data + 496, LABEL, 16) == 0) {
			blkno += 2;
			break;
		}
		++blkno;
	}
	return blkno;
}

struct path * parse_path(const char *path)
{
	char *end;
	int len;
	struct path *ret;
	char *p;
	char *p1;
	int slash_count = 0;
	if (path == NULL)
		return NULL;
	ret = malloc(sizeof(struct path));
	p = strdup(path);
	p1 = p;
	memset(ret, 0, sizeof(struct path));
	if (p[0] != '/')
		return NULL;
	while(p1[0] != '\0') {
		if(p1 != p) {
			while(p1[-1] == '/' && p1[0] == '/') {
				char *t = p1;
				while(t[0] != '\0') {
					t++;
					t[-1] = t[0];
				}
			}
		}
		if (p1[0] == '/')
			++slash_count;
		p1++;
	}
	if(slash_count > 2) {
		free(p);
		free(ret);
		return NULL;
	}
	len = strlen(p);
	end = strrchr(p, '/');
	if (len == 1) {
		strcpy(ret->directory, "/");
	} else if (slash_count == 1) {
		memcpy(ret->directory, p + 1, 15);
	} else {
		len = end - (p + 1);
		memcpy(ret->directory, p + 1, (len > 15 ? 15 : len));
		len = strlen(end);
		memcpy(ret->filename, end + 1, (len > 15 ? 15 : len));
	}
	free(p);
	return ret;
}

int init_fs(const char * image)
{
	rom_fh = fopen(image, "r");
	if (rom_fh == NULL) {
		return 0;
	}
	start_blk = find_fs(rom_fh);
	if (start_blk == 0) {
		fclose(rom_fh);
		rom_fh = NULL;
		return 0;
	}
	return 1;
}

struct file* fs_open(const char *filename)
{
	struct dir *d;
	struct direntry *entry;
	struct file *file = NULL;
	struct path *path = parse_path(filename);
	char dir[17] = {'/'};
	if (path && strcmp(path->filename, "") != 0) {
		strncpy(dir + 1, path->directory, 16);
		d = fs_opendir(dir);
		while((entry = fs_readdir(d)) != NULL) {
			if (strcmp(entry->filename, path->filename) == 0)
				break;
			free(entry);
		}
		free(d);
		if (entry != NULL) {
			file = malloc(sizeof(struct file));
			file->fp = 0;
			file->blkno = entry->location - LOCOFF;
			file->size = entry->size;
			free(entry);
		}
	}
	free(path);
	return file;
}

unsigned long fs_read(struct file* fp, char *buffer, int length)
{
	struct nand_block blk;
	unsigned long block;
	unsigned long offset;
	unsigned long read = 0;
	unsigned long left = MIN(length, fp->size - fp->fp);
	while (left > 0) {
		block = fp->fp / 512;
		offset = fp->fp % 512;
		read_nand(rom_fh, start_blk + fp->blkno + block, &blk);
		memcpy(buffer + read, blk.data + offset, MIN(512 - offset, left));
		read += MIN(512 - offset, left);
		fp->fp += MIN(512 - offset, left);
		left -= MIN(512 - offset, left);
	}
	return read;
}

struct dir* fs_opendir(const char* dir)
{
	struct path *path = parse_path(dir);
	struct dir *handle, *subdir;
	struct direntry *entry;
	if (path && strcmp(path->filename, "") == 0) {
		if (strcmp(path->directory, "/") == 0) {
			handle = malloc(sizeof(struct dir));
			handle->cidx = 0;
			handle->dir_id = -1;
			return handle;
		} else {
			subdir = fs_opendir("/");
			if (subdir == NULL)
				return NULL;
			while((entry = fs_readdir(subdir)) != NULL) {
				if (strcmp(entry->filename, path->directory) == 0)
					break;
				free(entry);
			}
			free(subdir);
			if (entry != NULL) {
				handle = malloc(sizeof(struct dir));
				handle->cidx = entry->location;
				handle->dir_id = entry->dir_id;
				free(entry);
				return handle;				
			}
		}
	}
	free(path);
	return NULL;
}

struct direntry * fs_readdir(struct dir *directory)
{
	struct nand_block blk;
	struct direntry *entry;
	unsigned long block, offset;
	entry = malloc(sizeof(struct direntry));
	block = (directory->cidx * 0x20) / 512;
	offset = (directory->cidx * 0x20) % 512;
	read_nand(rom_fh, start_blk + block, &blk);
	memcpy(entry, blk.data + offset, 32);
	entry->dir_id = ntohs(entry->dir_id);
	entry->dir_ptr = ntohs(entry->dir_ptr);
	entry->location = ntohl(entry->location);
	entry->size = ntohl(entry->size);
	if (directory->dir_id == -1) {
		if (entry->dir_id == 0xffff) {
			free(entry);
			entry = NULL;
		}
	} else {
		if (entry->dir_ptr != directory->dir_id) {
			free(entry);
			entry = NULL;
		}
	}
	if (entry != NULL)
		directory->cidx++;
	return entry;
}

void deinit_fs()
{
	fclose(rom_fh);
}

[jackyjkchen]

把扩展名从cpp改成c

[「已注销」]

--------------------Configuration: fs - Win32 Debug--------------------
Compiling...
filesystem.c
c:\复件 fs_dumper\filesystem.c(134) : warning C4018: '>' : signed/unsigned mismatch
Linking...
fs_dumper.obj : error LNK2001: unresolved external symbol "unsigned long __cdecl fs_read(struct file *,char *,int)" (?fs_read@@YAKPAUfile@@PADH@Z)
fs_dumper.obj : error LNK2001: unresolved external symbol _g_free
fs_dumper.obj : error LNK2001: unresolved external symbol "struct file * __cdecl fs_open(char const *)" (?fs_open@@YAPAUfile@@PBD@Z)
fs_dumper.obj : error LNK2001: unresolved external symbol _g_build_path
fs_dumper.obj : error LNK2001: unresolved external symbol "struct direntry * __cdecl fs_readdir(struct dir *)" (?fs_readdir@@YAPAUdirentry@@PAUdir@@@Z)
fs_dumper.obj : error LNK2001: unresolved external symbol "struct dir * __cdecl fs_opendir(char const *)" (?fs_opendir@@YAPAUdir@@PBD@Z)
fs_dumper.obj : error LNK2001: unresolved external symbol "void __cdecl deinit_fs(void)" (?deinit_fs@@YAXXZ)
fs_dumper.obj : error LNK2001: unresolved external symbol "struct path * __cdecl parse_path(char const *)" (?parse_path@@YAPAUpath@@PBD@Z)
fs_dumper.obj : error LNK2001: unresolved external symbol "int __cdecl init_fs(char const *)" (?init_fs@@YAHPBD@Z)
fs_dumper.obj : error LNK2001: unresolved external symbol _g_print
fs_dumper.obj : error LNK2001: unresolved external symbol _g_option_context_parse
fs_dumper.obj : error LNK2001: unresolved external symbol _g_option_context_add_main_entries
fs_dumper.obj : error LNK2001: unresolved external symbol _g_option_context_new
filesystem.obj : error LNK2001: unresolved external symbol _read_nand
filesystem.obj : error LNK2001: unresolved external symbol __imp__ntohl@4
filesystem.obj : error LNK2001: unresolved external symbol __imp__ntohs@4
Debug/fs.exe : fatal error LNK1120: 16 unresolved externals
执行 link.exe 时出错.

fs.exe - 1 error(s), 0 warning(s)

[xin_wu_hen]

在xmalloc之前，进行强制类型转换（为=号之前的变量类型）。一般来说，我们可以将任何类型的指针赋给void*,但是相反过程必须使用强制类型转换才可以。这是c++的一个标准。

[super_admi]

强制转换即可，不要换什么.c,.cpp。

比如char * the_string = NULL;
the_string = (char*)malloc(sizeof(char)*string_len);