I have been using the md5 implementation found in this page:
http://www.zedwood.com/article/121/cpp-md5-function
As it is it works fine. There is however this function:
// return hex representation of digest as string
std::string MD5::hexdigest() const
{
if (!finalized)
return "";
char buf[33];
for (int i=0; i<16; i++)
sprintf(buf+i*2, "%02x", digest[i]);
buf[32]=0;
return std::string(buf);
}
If I change sprintf to the safe version (sprintf_s), then I get an Access Violation Error at runtime. The only thing I change is the sprintf line, like this:
sprintf_s(buf+i*2, 33, "%02x", digest[i]);
It compiles fine but then I get the error. Any idea why ?
Since you pass an offset into your buffer, you also need to reduce the size you pass to snprintf_s. That is:
snprintf_s(buf+i*2, 33-2*i, "%02x", digest[i]);
Related
I am trying to send values from ADC through USB using "CDC_Transmit_FS()"
On the receiving side, I am receiving data using readline() and decoding the 'string' to 'int'
The code works fine but occasionally I receive for example, b'\x00234\n' instead of b'1234\n', which raises decoding error.
Do you know why does '\x' appear?
One more question is: Is there any smarter method to send ADC values through USB instead of converting int values to string?
I want to make the transmission faster.
thanks in advance!
uint32_t adcbuff[sample];
char endofpacket[5] = {'9', '9', '9', '9', '\n'};
char txbuff[sample*5];
while(1)
{
HAL_ADC_Start_DMA(&hadc2,(uint32_t*)adcbuff, sample);
for(i = 0; i < sample; i++)
{
sprintf (tempbuff, "%u\n", ((adcbuff[i] * 5000) / 0xFFFF)-2000);
strcat( txbuff,tempbuff);
}
strcat( txbuff,endofpacket);
CDC_Transmit_FS( (uint8_t*)txbuff, strlen(txbuff));
strcpy(txtbuff,"");
}
not enough rep to post as a comment
Usually \x is an indication of a hexadecimal value. Could it be that a non alphanumeric value is being received?
For troubleshooting, I would temporarily change
sprintf (tempbuff, "%u\n", ((adcbuff[i] * 5000) / 0xFFFF)-2000); to
sprintf (tempbuff, "%s\n", ((adcbuff[i] * 5000) / 0xFFFF)-2000); to see what kind of characters are being sent over. (Maybe sprintf to a tmp file instead.)
b'\x00234\n' - This means that first byte is 0! Not ASCII 0 = 0x30, but just 0.
Probably this is effect of strcat - after concatenating this function adds '\0' at the end of string.
Instead of using sprintf, just redirect stdout to USB-CDC and use printf:
int _write(int file, char *ptr, int len)
{
UNUSED(file);
CDC_Transmit_FS((uint8_t*)ptr, len);
while (hcdc->TxState != 0);
return len;
}
If you want to send all at once use setvbuf for stdout with _IOFBF and call fflush(stdout);
I'm just an amateur programmer...
And when reading, for the second time, and more than two years apart, kochan's "Programming in Objective-C", now the 6th ed., reaching the pointer chapter i tried to revive the old days when i started programming with C...
So, i tried to program a reverse C string function, using char pointers...
At the end i got the desired result, but... got also a very strange behavior, i cannot explain with my little programming experience...
First the code:
This is a .m file,
#import <Foundation/Foundation.h>
#import "*pathToFolder*/NSPrint.m"
int main(int argc, char const *argv[])
{
#autoreleasepool
{
char * reverseString(char * str);
char *ch;
if (argc < 2)
{
NSPrint(#"No word typed in the command line!");
return 1;
}
NSPrint(#"Reversing arguments:");
for (int i = 1; argv[i]; i++)
{
ch = reverseString(argv[i]);
printf("%s\n", ch);
//NSPrint(#"%s - %s", argv[i], ch);
}
}
return 0;
}
char * reverseString(char * str)
{
int size = 0;
for ( ; *(str + size) != '\0'; size++) ;
//printf("Size: %i\n", size);
char result[size + 1];
int i = 0;
for (size-- ; size >= 0; size--, i++)
{
result[i] = *(str + size);
//printf("%c, %c\n", result[i], *(str + size));
}
result[i] = '\0';
//printf("result location: %lu\n", result);
//printf("%s\n", result);
return result;
}
Second some notes:
This code is compiled in a MacBook Pro, with MAC OS X Maverick, with CLANG (clang -fobjc-arc $file_name -o $file_name_base)
That NSPrint is just a wrapper for printf to print a NSString constructed with stringWithFormat:arguments:
And third the strange behavior:
If I uncomment all those commented printf declarations, everything work just fine, i.e., all printf functions print what they have to print, including the last printf inside main function.
If I uncomment one, and just one, randomly chosen, of those comment printf functions, again everything work just fine, and I got the correct printf results, including the last printf inside main function.
If I leave all those commented printf functions as they are, I GOT ONLY BLANK LINES with the last printf inside main block, and one black line for each argument passed...
Worst, if I use that NSPrint function inside main, instead of the printf one, I get the desired result :!
Can anyone bring some light here please :)
You're returning a local array, that goes out of scope as the function exits. Dereferencing that memory causes undefined behavior.
You are returning a pointer to a local variable of the function that was called. When that function returns, the memory for the local variable becomes invalid, and the pointer returned is rubbish.
-(void)InitWithPwd:(char *)pPwd
{
char szResult[17];
//generate md5 checksum
CC_MD5(pPwd, strlen(pPwd),&szResult[0]);
szResult[16] = 0;
m_csPasswordHash[0]=0;
for(int i = 0;i < 16;i++)
{
char sz[3] = {'\0'};
//crash in blow row. The first pass is ok. The third pass crash.
//I can't understand.
sprintf(&sz[0],"%2.2x",szResult[i]);
strcat(m_csPasswordHash,sz);
}
m_csPasswordHash[32] = 0;
printf("pass:%s\n",m_csPasswordHash);
m_ucPacketType = 1;
}
I want to get the md5 of the password. But above code crash again and again. I can't understand why.
Your buffer (sz) is too small, causing sprintf() to generate a buffer overflow which leads to undefined behavior, in your case a crash.
Note that szResult[1] might be a negative value when viewed as an int (which happens when passing a char-type value to sprintf()), which can cause sprintf() to disregard your field width and precision directives in order to format the full value.
Here is an example showing this problem. The example code is written in C, but that shouldn't matter for this case.
This solves the problem by making sure the incoming data is considered unsigned:
sprintf(sz, "%02x", (unsigned char) szResult[i]);
I'm writing an objective-C program to deal with trajectories of Biomolecules with XCODE 4.3.1 and ARC. I need to read PDB files, i.e. parse large quantities of text formatted data. I'm very disappointed by NSString inefficiency and was trying to write a C-equivalent of componentsSeparatedByString:. The algorithm works just fine with NSString and NSMutableArrays, but i'm having a hard time using char* and char**.
Unfortunately, I'm getting an EXC_BAD_ACCESS error. The strange thing is that i get the error for i=68103 and j=68049 (does these number ring a bell for you ?), which means it worked for some time before crashing. The error is "static" (always block at the same (i,j) numbers). The array seems to work just fine(NSLog on its values before crash).
As it seems, I'm not very experienced with C-code and the subtlety behind pointers, but I would definitely be glad to hear your suggestions to make it work ! Thanks !
Heres the code :
+(char**) componentsSeparedByNewLineCEQUIV:(const char*)aChar:(int*)numWord
{ // char* aChar : my file, is typically 3 millions characters
int j=-1; //Last non space character
int i; //Scanned character
int len=strlen(aChar);
char** stringArray=malloc((*numWord)*sizeof(char*));
for (i=0;i<len; i++)
{ if (aChar[i]==10)
{
if ( j!=-1)
{
char* buffer2=malloc(i-j+1);
strcpy(buffer2, strndup(aChar+j, i-j));
stringArray[i]=malloc(sizeof(char)*strlen(buffer2)+1); //EXC_BAD_ACCESS HERE
strcpy(stringArray[i], buffer2);
}
j=-1;
}
else if (j==-1)
{j=i;}
}
if (j!=-1)
{ char* buffer2=malloc(i-j+1);
strcpy(buffer2, strndup(aChar+j, i-j));
stringArray[i]=malloc(strlen(buffer2)+1);
strcpy(stringArray[i], buffer2);
}
return stringArray;
}
You're probably not the first person to have this problem :)
Why not just use strtok?
PS What analysis showed that NSString was your problem?
I don't know why the error is at the line above of where it should be.However you are copying a string that is not allocated.
stringArray[i] is not allocated when you copy on it buffer2, allocate it:
if ( j!=-1)
{
char* buffer2=malloc(i-j+1);
strcpy(buffer2, strndup(aChar+j, i-j));
stringArray[i]=malloc(sizeof(char)*strlen(buffer2)+1); //EXC_BAD_ACCESS HERE
stringArray[i]=(char*)malloc( (strlen(buffer2)+1)*sizeof(char)); // Allocate the string
strcpy(stringArray[i], buffer2);
}
First: if Im not totaly wrong, but i think you are consuming at least 4-times as much memory as you need to:
You are using malloc for creating buffer2 and also using strndup for getting the wanted chars. strndup does exactly what you want, but in one step. char* buffer2 = strndup(aChar+j, i-j) should be your first step. Even worse in the next two line you are essential doing the same again. So i think what you are really want is stringArray[i] = strndup(aChar+j, i-j). To look at memory Problems: all the functions use errno to indicate memory allocating failure.
Second: Your functions does not return the number of components, so your stringArray may contain some garbage without knowing.
Third: strlen is expensive and you do not need it, just use for(int i = 0; aChar[i] != '\0'; i++)
Update for everyone who might be interested : this is a working version, using strtok which can be useful, although i'm still interested in response on my code.
This code have been tested 5 times faster (125ms vs 581ms) than [astring componentsSeparatedByString:#"\n"] ...
+(char**)componentsSeparatedByNewLine:(const char*)aChar:(int*)numWord
{
int i;
int j=0;
int len = strlen(aChar);
*numWord=1;
for (i=0;i<len; i++)
{
if (aChar[i]==10) *numWord=*numWord+1; //change 10 for any other character (ASCII for space)
}
char** stringArray=malloc((*numWord)*sizeof(char*));
char* pch;
char* aChar2=malloc(len+1);
strcpy(aChar2,aChar);
pch = strtok(aChar2,"\n");
while (pch != NULL)
{
stringArray[j]=(char*)malloc( (strlen(pch)+1)*sizeof(char));
strcpy(stringArray[j], pch);
//NSLog(#"%s",stringArray[j]);
j=j+1;
pch = strtok (NULL, "\n");
}
return stringArray;
}
I'm trying to allow users to simply hit Enter without typing anything, and use this to mean accepting a default value. scanf isn't doing what I want and the app still 'blocks': the next line of code doesn't run.
The only way is to actually type something THEN press Enter.
I tried using NSFileHandle and fileHandleWithStandardInput; however, it seems that the user is now forced to hit Ctrl-D to indicate EOF.
Someone suggested using fgets, but I cannot work out what to pass as 3rd parameter (of FILE* type). Tried stdin but it doesn't 'block'.
How do I accept input from a user, using Objective-C, and at the same time allow the user to simply hit Enter without being forced to type anything? How do I read a single line, even if that line is blank?
Assuming the code doesn't block and the next line runs immediately (as you seemed to indicate early in the question and in a comment), you have a common problem when mixing non-line-based and line-based input.
What happens is you have a newline left in the buffer, and fgets sees that, reads it, and returns, instead of doing what you really want: ignoring it, and then reading a line.
The solution is to simply do the ignoring part yourself, and then call fgets:
#include <stdio.h>
#include <string.h>
FILE* ignoreline(FILE* stream) {
for (int c; (c = fgetc(stream)) != EOF;) {
if (c == '\n') break;
}
return stream;
}
void example_use() {
char buf[1000];
ignoreline(stdin);
fgets(buf, sizeof buf, stdin);
// or, since it returns the stream, can be more compact:
fgets(buf, sizeof buf, ignoreline(stdin));
}
int main() { // error handling omitted
int n;
printf("Enter a number: ");
scanf("%d", &n);
char buf[1000];
printf("Enter a line: ");
ignoreline(stdin); // comment this line and compare the difference
fgets(buf, sizeof buf, stdin);
*strchr(buf, '\n') = '\0';
printf("You entered '%s'.\n", buf);
return 0;
}
Note that it is also common and encouraged to "pair" the ignoreline with the scanf (or other non-line-based input) to turn that into line-based input. You may want to modify it, in that case, so you can tell the difference between input of "42 abc" and "42" (in the "Enter a number" case). Some people just use fgets everywhere, then parse that line with sscanf, and while that works, it's not necessary.
I use getch(); in library conio.h
simply the program waits for any key to be pressed
If you're using Windows, you can use the ReadConsoleInput function (see MSDN for more on this) :
INPUT_RECORD keyin;
DWORD r;
while (ReadConsoleInput(GetStdHandle(STD_INPUT_HANDLE),&keyin,1,&r)) {
if (keyin.EventType!=KEY_EVENT) continue;
if (keyin.Event.KeyEvent.wVirtualKeyCode==VK_SPACE) break; ///use these VK codes to get any key's input
if (keyin.Event.KeyEvent.wVirtualKeyCode==VK_F1)
{
printf("You pressed F1\n");
}
if (keyin.Event.KeyEvent.wVirtualKeyCode==VK_F2)
{
printf("You pressed F2\n",);
}
}//end while loop
You don't need to hit enter after each key then.This works like a dream for me...
use getchar() to take input without using scanf function...