fmemopen_windows

a lib to provide FILE* handler based on memory backend for fread,fwrite etc just like fmemopen on linux on windows.

Usage

1.include the header.
2.include the libary depend on your platform32/64.
3.using fmemopen.

usage sample:

#include <stdio.h>
#include "libfmemopen.h"

int main(){
	FILE * fh;
	char buf[1024] = "jacksonsonsosnososnsljgweoigjiedjgkdrjshnjklfcgsdntildhgd fjklhndrhpadk thiohkaerheil ghksbjd ghbjcghkwe4pt hphq tgjh";
	//put your stuff in buffer
	fh = fmemopen(buf, 1024, "wb");
	printf("FileHandler:%d\n", fh);
	getchar();
	fseek(fh, 0, SEEK_SET);
	char * bux[1024];
	int readbytes = fread(bux, 1, 1024, fh);
	printf("\nbuffer:%s\n", bux);
	printf("Readed_bytes:%d\n", readbytes);
	getchar();
	fclose(fh);//don't forgot fclose it,call fclose on a handler created by fmemopen_windows libary will automatically free it(include deep layer).
	return 0;
}

A bad example:

there may got some security risk in this version,look the code below.I'll dig it later.

#include <stdio.h>
#include "libfmemopen.h"

int main(){
	FILE * fh;
	char buf[1024] = "jacksonsonsosnososnsljgweoigjiedjgkdrjshnjklfcgsdntildhgd fjklhndrhpadk thiohkaerheil ghksbjd ghbjcghkwe4pt hphq tgjh";
	//put your stuff in buffer
	fh = fmemopen(buf, 1024, "wb");
	printf("FileHandler:%d\n", fh);
	getchar();
	fseek(fh, 0, SEEK_SET);
	char ddbuf[1028] = "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaABB";
	int johnlet=fwrite(ddbuf, 1028, 1, fh);
	printf("actually_write_long:%d\n", johnlet);
	fseek(fh, 0, SEEK_SET);
	char * bux[1030];
	int readbytes = fread(bux, 1, 1030, fh);
	printf("\nbuffer:%s\n", bux);
	printf("Readed_bytes:%d\n", readbytes);
	printf("\n\nTheOriginalBuf:%s", buf);
	getchar();
	fclose(fh);//don't forgot fclose it,call fclose on a handler created by fmemopen_windows libary will automatically free it(include deep layer).
	return 0;
}

#include <stdio.h>
#include "libfmemopen.h"

int main(){
	FILE * fh;
	char buf[1024] = "jacksonsonsosnososnsljgweoigjiedjgkdrjshnjklfcgsdntildhgd fjklhndrhpadk thiohkaerheil ghksbjd ghbjcghkwe4pt hphq tgjh";
	//put your stuff in buffer
	fh = fmemopen(buf, 1024, "wb");
	printf("FileHandler:%d\n", fh);
	//sizer

	fseek(fh, 0, SEEK_END);   ///将文件指针移动文件结尾
	long size = ftell(fh);
	printf("size:%d\n", size);
	//size
	getchar();
	fseek(fh, 0, SEEK_SET);
	char ddbuf[1028] = "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaABBCCDDEE";
	int johnlet=fwrite(ddbuf, 1028, 1, fh);
	//size
	printf("actually_write_long:%d\n", johnlet);
	fseek(fh, 0, SEEK_END);   ///将文件指针移动文件结尾
	size = ftell(fh);
	printf("size:%d\n", size);
	//size
	fflush(fh);
	//size
	fseek(fh, 0, SEEK_END);   ///将文件指针移动文件结尾
	size = ftell(fh);
	printf("size:%d\n", size);
	//size
	fseek(fh, 0, SEEK_SET);

	char * bux[1030];
	int readbytes = fread(bux, 1, 1030, fh);
	printf("\nbuffer:%s\n", bux);
	printf("Readed_bytes:%d\n", readbytes);
	printf("\n\nTheOriginalBuf:%s", buf);
	getchar();
	fclose(fh);//don't forgot fclose it,call fclose on a handler created by fmemopen_windows libary will automatically free it(include deep layer).
	return 0;
}

during these days I've been try alot way to simulate fmemopen on windows,this lib is the best solution I found at the end.

the way I think we can done this:

completely rewrite fread,fwrite.... X
mmioOpen

a good way to perform pure memory File I/O,but the return handler is HMMIO cannot cast to FILE* https://docs.microsoft.com/en-us/windows/win32/multimedia/performing-memory-file-i-o and You must call mmioClose to close a file opened by using mmioOpen. Open files are not automatically closed when an application exits. and seems like poor support after win2k.

using ramdisk

need to load driver,and perform 'disk' format etc,too heavy.

using _open

https://docs.microsoft.com/zh-tw/previous-versions/z0kc8e3z%28v%3dvs.120%29 this is the way,due to the lack support of windows kernel,we have to create a temp file on disk then use _open to create a FILE* type handler for use,and by control the create of temp file,we can avoid any actually disk write operation to the temp file(you fmemopen a 100mb file in memory and it's still 0 bits on disk),it's like a pointer which we must need due to the windows kernel.

with few experiments the _open is optional way,but it's deprecated and microsoft say they have a newer secure version _sopen_s and _wsopen_s,so this libary will use _sopen_s.

across the description by msdn,the _sopen_s still got a chance to write things to disk,when memory not enough,so you may better not cache your secret key etc in it.

uplinkcoder / fmemopen_windows Goto Github PK