Thread: problem with data in allocated memory

hi,

i have a problem in storing the data in allocated memory using malloc.

i have structure to store huge data form the serial port.

Code:

typedef struct FileData {		
		unsigned char  *FRdata;
		struct FileData *next;
}FileData;

/*I store the data in FileData->FRdata, by allocating sufficient memory to it*/

Datacur->FRdata=(char *)malloc(sizeof(max_bytes));

for(j=0;bytes_to_read>0;j++,bytes_to_read--)
	Datacur->FRdata[j]=*Ftemp++;
Datacur->next=NULL;

i have to write the raw data from the serial port in to file after converting the raw into its format[ the data format is usually float type].

when i print few data before opening a file

Code:

j=0;
printf("read");
while(j<10){
printf("%02x ",Datahead->FRdata[j++]);
}

there is no change in the data .

The problem is after , file is opened

Code:

 fptr=fopen(Surveyname,"wt");

the data in the allocated memory{Datahead->FRdata[} has changed { the data that is written to file is different to that of original data.}

where cud be the malicious alteration hapened.

any help on this.