Reading image into char array

[loolyn]

Hi All.

I need to read an image to char array with C++. I have written the following code for it, but it seems that the code does not read the entire image, it just reads the part of it. Can someone hint why, or give some better solution for how to read an image into char array?

std::fstream image;
image.open("C:\\bbb.bmp");

image.seekg (0, ios::end);
int n = image.tellg();
image.seekg (0, ios::beg);

char* res = new char[n];

image.read(res, n);

Thanks behorehand.

[helios]

Open the file as binary by passing std::ios::binary to std::fstream::open().

[loolyn]

Thanks for the reply Helios.

I modified the code to be like this:

std::fstream image;
image.open("C:\\bbb.bmp", std::ios_base::binary);

image.seekg (0, ios::end);
int n = image.tellg();
image.seekg (0, ios::beg);

char* res = new char[n];
for(int i = 0; i < n; i++)
res[i] = '5';

bool bit = image.eof();

image.read(res, n);

But now another issue arose. I don't know why the value of "n" becomes "-1".

[helios]

Check that the file was opened.

[loolyn]

I used ifstream instead of fstream, and that worked.

Thanks a lot.

[priyesh16]

i am a total c c++ nubi..i am practising in eclipse cde using mingw compiler


i wanted to load a bitmap(actually any image will do .bmp looked simpler) image into a matrix ..something like matlab's imread().. i googled a small code but i cant view the values in the matrix..

plz help me with this code..or new code if possible


ignore all the comments b'coz i wrote it for my own understanding
#include <iostream.h>
#include <fstream.h>
#include <conio.h>
//#include <stdio.h>



typedef unsigned long LONG;
typedef unsigned short WORD;
typedef unsigned long DWORD;

typedef struct tagBITMAPFILEHEADER
{
uint16_t bfType; //specifies the file type
uint32_t bfSize; //specifies the size in bytes of the bitmap file
uint16_t bfReserved1; //reserved; must be 0
uint16_t bfReserved2; //reserved; must be 0
uint32_t bfOffBits; //species the offset in bytes from the bitmapfileheader to the bitmap bits
}BITMAPFILEHEADER;

//the bftype field checks to see if you are infact loading a bmp file, and if you are the field should be 0x4D42.

//Now we need to create our bitmapinfoheader struct. This holds info about our bitmap(self explainitory).

typedef struct tagBITMAPINFOHEADER
{
uint32_t biSize; //specifies the number of bytes required by the struct/header
uint32_t biWidth; //specifies width in pixels
uint32_t biHeight; //species height in pixels
uint16_t biPlanes; //specifies the number of color planes, must be 1
uint16_t biBitCount; //specifies the number of bit per pixel
uint32_t biCompression;//specifies the type of compression
uint32_t biSizeImage; //size of image in bytes
int32_t biXPelsPerMeter; //number of pixels per meter in x axis
int32_t biYPelsPerMeter; //number of pixels per meter in y axis
uint32_t biClrUsed; //number of colors used by th ebitmap
uint32_t biClrImportant; //number of colors that are important
}BITMAPINFOHEADER;

int imagesize;
//Now on to loading our Bitmap

uint8_t *LoadBitmapFile(char *filename, BITMAPINFOHEADER *bitmapInfoHeader)
{
FILE *filePtr; //our file pointer
BITMAPFILEHEADER bitmapFileHeader; //our bitmap file header
uint8_t *bitmapImage; //store image data
int imageIdx=0; //image index counter
unsigned char tempRGB; //our swap variable

//open filename in read binary mode
filePtr = fopen(filename,"rb");
if (filePtr == NULL)
{
cout<<"couldn't open the file";
return NULL;
}
//read the bitmap file header
fread(&bitmapFileHeader, sizeof(BITMAPFILEHEADER),1,filePtr);

//cout<<bitmapFileHeader.bfType;
//cout<<bitmapFileHeader.bfOffBits;
//verify that this is a bmp file by check bitmap id
if (bitmapFileHeader.bfType !=0x4D42)
{
cout<<bitmapFileHeader.bfType;
cout<<"some problem with bf type";
fclose(filePtr);
return NULL;
}
//printf("Height: %d\n", bitmapInfoHeader->biHeight);
//read the bitmap info header
fread(bitmapInfoHeader, sizeof(BITMAPINFOHEADER),1,filePtr);
//int i;
//for(i=0;i<sizeof(BITMAPINFOHEADER);i++)
//{
// cout<<&bitmapInfoHeader[i]<<"    ";
//}
//cout<<"\n i="<<i <<"\n";

//printf("Height: %d\n", bitmapInfoHeader->biHeight);
//cout<<"bi planes"<<bitmapInfoHeader->biPlanes<<"  ";
//fseek(filePtr,0x16, SEEK_SET);
//cout<<"bi width"<<bitmapInfoHeader->biWidth<<"  ";
//cout<<"bi size"<<bitmapInfoHeader->biSize<<"  ";
//printf("biplanes  %x  ", bitmapInfoHeader->biPlanes);
//cout<<"bi bitcount"<<bitmapInfoHeader->biBitCount<<"  ";
//cout<<"bi compression"<<bitmapInfoHeader->biCompression<<"  ";
//move file point to the begging of bitmap data
//rewind(filePtr);
fseek(filePtr, bitmapFileHeader.bfOffBits, SEEK_SET);

//allocate enough memory for the bitmap image data
bitmapImage = (uint8_t*)malloc(bitmapInfoHeader->biSizeImage);

//verify memory allocation
if (!bitmapImage)
{
free(bitmapImage);
cout<<"couldnt create memory location";
fclose(filePtr);
return NULL;
}

//read in the bitmap image data
fread(bitmapImage,bitmapInfoHeader->biSizeImage,1,filePtr);

//make sure bitmap image data was read
if (bitmapImage == NULL)
{
cout<<"bitmap image not read";
fclose(filePtr);
return NULL;
}

//swap the r and b values to get RGB (bitmap is BGR)
imagesize = bitmapInfoHeader->biSizeImage;
//cout<<bitmapInfoHeader->biSizeImage;
for (imageIdx = 0;imageIdx < bitmapInfoHeader->biSizeImage;imageIdx+=3)
{
tempRGB = bitmapImage[imageIdx];
bitmapImage[imageIdx] = bitmapImage[imageIdx + 2];
bitmapImage[imageIdx + 2] = tempRGB;
}

//close file and return bitmap iamge data
fclose(filePtr);
return bitmapImage;
}


//Now to make use of all of this:

int main()
{
BITMAPINFOHEADER bitmapInfoHeader;
uint8_t *bitmapData;
fflush(stdin);
bitmapData = LoadBitmapFile("d:\\lena.bmp",&bitmapInfoHeader);
//now do what you want with it, later on i will show you how to display it in a normal window
//cout<<"int"<<sizeof(int)<< "short"<<sizeof(short)<<"long"<<sizeof(long);
for (int imageIdx = 0;imageIdx < 1000 ;imageIdx++)
{
cout<<bitmapData[imageIdx];
}
getch();
return 0;
}