I want to use regex on a binary file, which contains 0 bytes, which renders me unable to use a string. I'm using a char array, and I'm able to use regex on the char array.
Buffer is a copy of the file mapped into memory, and read is the total size. This code works, but now I want to get the result back from the function. How do I do this?
if(std::regex_search(buffer, buffer + read, *params->pattern))
{
std::cout << "Found.";
}
I did not test this but it should work..
auto it = std::cregex_iterator(&buffer[0], &buffer[read], *params->pattern);
for (int i = 0; i < it->size(); ++i)
{
const char* str = (*it)[i].str();
size_t size = (*it)[i].length();
std::cout.write(str, size);
}
I've tested this only on regular strings.. Not strings containing null chars. I don't see why it shouldn't work though because it does return a sequence of chars and the length of said sequence.
Related
I'm working on an API for an embedded device, and need to display an image generated (by the API). The screen attached to the device allows me to render bitmaps, with data stored as unsigned char image[] = { 0B00000000, 0B00001111, 0B11111110... }.
What is the easiest way to deserialize a string in whatever format needed?
My approach was to create a stringstream, separate by comma and push to vector<char>. However, the function to render bitmaps will only accept char, and from what I can find online it seems to be quite difficult to convert it. Ideally, I'd rather not use a vector at all, as including it adds several kbs to the project, which is limited in size by both the download speed of the embedded device (firmware is transferred by EDGE) and the onboard storage.
From the comments, it sounds like you want to convert a string composed of a series of "0b00000000" style literals, comma separated, into an array of their actual values. The way I would do this is to:
Get the number of bytes in the image (I assume this is known from the string length?).
Create a std::vector of unsigned char to hold the results.
For each byte in the input, construct a std::bitset from the string value, and then get its actual value.
Here's a code example. Since you have said you'd rather not use vector I have used C-style arrays and strings:
#include <bitset>
#include <cstring>
#include <iostream>
#include <memory>
int main() {
auto input = "0b00000000,0b00001111,0b11111111";
auto length = strlen(input);
// Get the number of bytes from the string length. Each byte takes 10 chars
// plus a comma separator.
int size = (length + 1) / 11;
// Allocate memory to hold the result.
std::unique_ptr<unsigned char[]> bytes(new unsigned char[size]);
// Populate each byte individually.
for (int i = 0; i < size; ++i) {
// Create the bitset. The stride is 11, and skip the first 2 characters
// to skip the 0b prefix.
std::bitset<8> bitset(input + 2 + i * 11, 8);
// Store the resulting byte.
bytes[i] = bitset.to_ulong();
}
// Now loop back over each byte, and output it to confirm the result.
for (int i = 0; i < size; ++i) {
std::cout << "0b" << std::bitset<8>(bytes[i]) << std::endl;
}
}
i have a buffer
char buffer[size];
which i am using to store the file contents of a stream(suppose pStream here)
HRESULT hr = pStream->Read(buffer, size, &cbRead );
now i have all the contents of this stream in buffer which is of size(suppose size here). now i know that i have two strings
"<!doctortype html" and ".html>"
which are present somewhere (we don't their loctions) inside the stored contents of this buffer and i want to store just the contents of the buffer from the location
"<!doctortype html" to another string ".html>"
in to another buffer2[SizeWeDontKnow] yet.
How to do that ??? (actually contents from these two location are the contents of a html file and i want to store the contents of only html file present in this buffer). any ideas how to do that ??
You can use strnstr function to find the right position in your buffer. After you've found the starting and ending tag, you can extract the text inbetween using strncpy, or use it in place if the performance is an issue.
You can calculate needed size from the positions of the tags and the length of the first tag nLength = nPosEnd - nPosStart - nStartTagLength
Look for HTML parsers for C/C++.
Another way is to have a char pointer from the start of the buffer and then check each char there after. See if it follows your requirement.
If that's the only operation which operates on HTML code in your app, then you could use the solution I provided below (you can also test it online - here). However, if you are going to do some more complicated parsing, then I suggest using some external library.
#include <iostream>
#include <cstdio>
#include <cstring>
using namespace std;
int main()
{
const char* beforePrefix = "asdfasdfasdfasdf";
const char* prefix = "<!doctortype html";
const char* suffix = ".html>";
const char* postSuffix = "asdasdasd";
unsigned size = 1024;
char buf[size];
sprintf(buf, "%s%sTHE STRING YOU WANT TO GET%s%s", beforePrefix, prefix, suffix, postSuffix);
cout << "Before: " << buf << endl;
const char* firstOccurenceOfPrefixPtr = strstr(buf, prefix);
const char* firstOccurenceOfSuffixPtr = strstr(buf, suffix);
if (firstOccurenceOfPrefixPtr && firstOccurenceOfSuffixPtr)
{
unsigned textLen = (unsigned)(firstOccurenceOfSuffixPtr - firstOccurenceOfPrefixPtr - strlen(prefix));
char newBuf[size];
strncpy(newBuf, firstOccurenceOfPrefixPtr + strlen(prefix), textLen);
newBuf[textLen] = 0;
cout << "After: " << newBuf << endl;
}
return 0;
}
EDIT
I get it now :). You should use strstr to find the first occurence of the prefix then. I edited the code above, and updated the link.
Are you limited to C, or can you use C++?
In the C library reference there are plenty of useful ways of tokenising strings and comparing for matches (string.h):
http://www.cplusplus.com/reference/cstring/
Using C++ I would do the following (using buffer and size variables from your code):
// copy char array to std::string
std::string text(buffer, buffer + size);
// define what we're looking for
std::string begin_text("<!doctortype html");
std::string end_text(".html>");
// find the start and end of the text we need to extract
size_t begin_pos = text.find(begin_text) + begin_text.length();
size_t end_pos = text.find(end_text);
// create a substring from the positions
std::string extract = text.substr(begin_pos,end_pos);
// test that we got the extract
std::cout << extract << std::endl;
If you need C string compatibility you can use:
char* tmp = extract.c_str();
I wrote a very simple encryption program to practice c++ and i came across this weird behavior. When i convert my char* array to a string by setting the string equal to the array, then i get a wrong string, however when i create an empty string and add append the chars in the array individually, it creates the correct string. Could someone please explain why this is happening, i just started programming in c++ last week and i cannot figure out why this is not working.
Btw i checked online and these are apparently both valid ways of converting a char array to a string.
void expandPassword(string* pass)
{
int pHash = hashCode(pass);
int pLen = pass->size();
char* expPass = new char[264];
for (int i = 0; i < 264; i++)
{
expPass[i] = (*pass)[i % pLen] * (char) rand();
}
string str;
for (int i = 0; i < 264; i++)
{
str += expPass[i];// This creates the string version correctly
}
string str2 = expPass;// This creates much shorter string
cout <<str<<"\n--------------\n"<<str2<<"\n---------------\n";
delete[] expPass;
}
EDIT: I removed all of the zeros from the array and it did not change anything
When copying from char* to std::string, the assignment operator stops when it reaches the first NULL character. This points to a problem with your "encryption" which is causing embedded NULL characters.
This is one of the main reasons why encoding is used with encrypted data. After encryption, the resulting data should be encoded using Hex/base16 or base64 algorithms.
a c-string as what you are constructing is a series of characters ending with a \0 (zero) ascii value.
in the case of
expPass[i] = (*pass)[i % pLen] * (char) rand();
you may be inserting \0 into the array if the expression evaluates to 0, as well as you do not append a \0 at the end of the string either to assure it being a valid c-string.
when you do
string str2 = expPass;
it can very well be that the string gets shorter since it gets truncated when it finds a \0 somewhere in the string.
This is because str2 = expPass interprets expPass as a C-style string, meaning that a zero-valued ("null") byte '\0' indicates the end of the string. So, for example, this:
char p[2];
p[0] = 'a';
p[1] = '\0';
std::string s = p;
will cause s to have length 1, since p has only one nonzero byte before its terminating '\0'. But this:
char p[2];
p[0] = 'a';
p[1] = '\0';
std::string s;
s += p[0];
s += p[1];
will cause s to have length 2, because it explicitly adds both bytes to s. (A std::string, unlike a C-style string, can contain actual null bytes — though it's not always a good idea to take advantage of that.)
I guess the following line cuts your string:
expPass[i] = (*pass)[i % pLen] * (char) rand();
If rand() returns 0 you get a string terminator at position i.
.
unsigned int fname_length = 0;
//fname length equals 30
file.read((char*)&fname_length,sizeof(unsigned int));
//fname contains random data as you would expect
char *fname = new char[fname_length];
//fname contains all the data 30 bytes long as you would expect, plus 18 bytes of random data on the end (intellisense display)
file.read((char*)fname,fname_length);
//m_material_file (std:string) contains all 48 characters
m_material_file = fname;
// count = 48
int count = m_material_file.length();
now when trying this way, intellisense still shows the 18 bytes of data after setting the char array to all ' ' and I get exactly the same results. even without the file read
char name[30];
for(int i = 0; i < 30; ++i)
{
name[i] = ' ';
}
file.read((char*)fname,30);
m_material_file = name;
int count = m_material_file.length();
any idea whats going wrong here, its probably something completely obvious but im stumped!
thanks
Sounds like the string in the file isn't null-terminated, and intellisense is assuming that it is. Or perhaps when you wrote the length of the string (30) into the file, you didn't include the null character in that count. Try adding:
fname[fname_length] = '\0';
after the file.read(). Oh yeah, you'll need to allocate an extra character too:
char * fname = new char[fname_length + 1];
I guess that intellisense is trying to interpret char* as C string and is looking for a '\0' byte.
fname is a char* so both the debugger display and m_material_file = fname will be expecting it to be terminated with a '\0'. You're never explicitly doing that, but it just happens that whatever data follows that memory buffer has a zero byte at some point, so instead of crashing (which is a likely scenario at some point), you get a string that's longer than you expect.
Use
m_material_file.assign(fname, fname + fname_length);
which removes the need for the zero terminator. Also, prefer std::vector to raw arrays.
std::string::operator=(char const*) is expecting a sequence of bytes terminated by a '\0'. You can solve this with any of the following:
extend fname by a character and add the '\0' explicitly as others have suggested or
use m_material_file.assign(&fname[0], &fname[fname_length]); instead or
use repeated calls to file.get(ch) and m_material_file.push_back(ch)
Personally, I would use the last option since it eliminates the explicitly allocated buffer altogether. One fewer explicit new is one fewer chance of leaking memory. The following snippet should do the job:
std::string read_name(std::istream& is) {
unsigned int name_length;
std::string file_name;
if (is.read((char*)&name_length, sizeof(name_length))) {
for (unsigned int i=0; i<name_length; ++i) {
char ch;
if (is.get(ch)) {
file_name.push_back(ch);
} else {
break;
}
}
}
return file_name;
}
Note:
You probably don't want to use sizeof(unsigned int) to determine how many bytes to write to a binary file. The number of bytes read/written is dependent on the compiler and platform. If you have a maximum length, then use it to determine the specific byte size to write out. If the length is guaranteed to fewer than 255 bytes, then only write a single byte for the length. Then your code will not depend on the byte size of intrinsic types.
Hello I have a chunk of memory (allocated with malloc()) that contains bits (bit literal), I'd like to read it as an array of char, or, better, I'd like to printout the ASCII value of 8 consecutively bits of the memory.
I have allocated he memory as char *, but I've not been able to take characters out in a better way than evaluating each bit, adding the value to a char and shifting left the value of the char, in a loop, but I was looking for a faster solution.
Thank you
What I've wrote for now is this:
for allocation:
char * bits = (char*) malloc(1);
for writing to mem:
ifstream cleartext;
cleartext.open(sometext);
while(cleartext.good())
{
c = cleartext.get();
for(int j = 0; j < 8; j++)
{ //set(index) and reset(index) set or reset the bit at bits[i]
(c & 0x80) ? (set(index)):(reset(index));//(*ptr++ = '1'):(*ptr++='0');
c = c << 1;
}..
}..
and until now I've not been able to get character back, I only get the bits printed out using:
printf("%s\n" bits);
An example of what I'm trying to do is:
input.txt contains the string "AAAB"
My program would have to write "AAAB" as "01000001010000010100000101000010" to memory
(it's the ASCII values in bit of AAAB that are 65656566 in bits)
Then I would like that it have a function to rewrite the content of the memory to a file.
So if memory contains again "01000001010000010100000101000010" it would write to the output file "AAAB".
int numBytes = 512;
char *pChar = (char *)malloc(numBytes);
for( int i = 0; i < numBytes; i++ ){
pChar[i] = '8';
}
Since this is C++, you can also use "new":
int numBytes = 512;
char *pChar = new char[numBytes];
for( int i = 0; i < numBytes; i++ ){
pChar[i] = '8';
}
If you want to visit every bit in the memory chunk, it looks like you need std::bitset.
char* pChunk = malloc( n );
// read in pChunk data
// iterate over all the bits.
for( int i = 0; i != n; ++i ){
std::bitset<8>& bits = *reinterpret_cast< std::bitset<8>* >( pByte );
for( int iBit = 0; iBit != 8; ++iBit ) {
std::cout << bits[i];
}
}
I'd like to printout the ASCII value of 8 consecutively bits of the memory.
The possible value for any bit is either 0 or 1. You probably want at least a byte.
char * bits = (char*) malloc(1);
Allocates 1 byte on the heap. A much more efficient and hassle-free thing would have been to create an object on the stack i.e.:
char bits; // a single character, has CHAR_BIT bits
ifstream cleartext;
cleartext.open(sometext);
The above doesn't write anything to mem. It tries to open a file in input mode.
It has ascii characters and common eof or \n, or things like this, the input would only be a textfile, so I think it should only contain ASCII characters, correct me if I'm wrong.
If your file only has ASCII data you don't have to worry. All you need to do is read in the file contents and write it out. The compiler manages how the data will be stored (i.e. which encoding to use for your characters and how to represent them in binary, the endianness of the system etc). The easiest way to read/write files will be:
// include these on as-needed basis
#include <algorithm>
#include <iostream>
#include <iterator>
#include <fstream>
using namespace std;
// ...
/* read from standard input and write to standard output */
copy((istream_iterator<char>(cin)), (istream_iterator<char>()),
(ostream_iterator<char>(cout)));
/*-------------------------------------------------------------*/
/* read from standard input and write to text file */
copy(istream_iterator<char>(cin), istream_iterator<char>(),
ostream_iterator<char>(ofstream("output.txt"), "\n") );
/*-------------------------------------------------------------*/
/* read from text file and write to text file */
copy(istream_iterator<char>(ifstream("input.txt")), istream_iterator<char>(),
ostream_iterator<char>(ofstream("output.txt"), "\n") );
/*-------------------------------------------------------------*/
The last remaining question is: Do you want to do something with the binary representation? If not, forget about it. Else, update your question one more time.
E.g: Processing the character array to encrypt it using a block cipher
/* a hash calculator */
struct hash_sha1 {
unsigned char operator()(unsigned char x) {
// process
return rc;
}
};
/* store house of characters, could've been a vector as well */
basic_string<unsigned char> line;
/* read from text file and write to a string of unsigned chars */
copy(istream_iterator<unsigned char>(ifstream("input.txt")),
istream_iterator<char>(),
back_inserter(line) );
/* Calculate a SHA-1 hash of the input */
basic_string<unsigned char> hashmsg;
transform(line.begin(), line.end(), back_inserter(hashmsg), hash_sha1());
Something like this?
char *buffer = (char*)malloc(42);
// ... put something into the buffer ...
printf("%c\n", buffer[0]);
But, since you're using C++, I wonder why you bother with malloc and such...
char* ptr = pAddressOfMemoryToRead;
while(ptr < pAddressOfMemoryToRead + blockLength)
{
char tmp = *ptr;
// temp now has the char from this spot in memory
ptr++;
}
Is this what you are trying to achieve:
char* p = (char*)malloc(10 * sizeof(char));
char* p1 = p;
memcpy(p,"abcdefghij", 10);
for(int i = 0; i < 10; ++i)
{
char c = *p1;
cout<<c<<" ";
++p1;
}
cout<<"\n";
free(p);
Can you please explain in more detail, perhaps including code? What you're saying makes no sense unless I'm completely misreading your question. Are you doing something like this?
char * chunk = (char *)malloc(256);
If so, you can access any character's worth of data by treating chunk as an array: chunk[5] gives you the 5th element, etc. Of course, these will be characters, which may be what you want, but I can't quite tell from your question... for instance, if chunk[5] is 65, when you print it like cout << chunk[5];, you'll get a letter 'A'.
However, you may be asking how to print out the actual number 65, in which case you want to do cout << int(chunk[5]);. Casting to int will make it print as an integer value instead of as a character. If you clarify your question, either I or someone else can help you further.
Are you asking how to copy the memory bytes of an arbitrary struct into a char* array? If so this should do the trick
SomeType t = GetSomeType();
char* ptr = malloc(sizeof(SomeType));
if ( !ptr ) {
// Handle no memory. Probably should just crash
}
memcpy(ptr,&t,sizeof(SomeType));
I'm not sure I entirely grok what you're trying to do, but a couple of suggestions:
1) use std::vector instead of malloc/free and new/delete. It's safer and doesn't have much overhead.
2) when processing, try doing chunks rather than bytes. Even though streams are buffered, it's usually more efficient grabbing a chunk at a time.
3) there's a lot of different ways to output bits, but again you don't want a stream output for each character. You might want to try something like the following:
void outputbits(char *dest, char source)
{
dest[8] = 0;
for(int i=0; i<8; ++i)
dest[i] = source & (1<<(7-i)) ? '1':'0';
}
Pass it a char[9] output buffer and a char input, and you get a printable bitstring back. Decent compilers produce OK output code for this... how much speed do you need?