c++ visual studio 2017 reading png dimension through header data
Hello i have problem to read out the correct data of png dimesnion size
unsigned width = 0;
unsigned height = 0;
bool output_json = false;
std::ifstream in(filepath, std::ios_base::binary | std::ios_base::in);
if (in.is_open())
{
in.seekg(16, std::ios_base::cur);
in.read((char *)&width, 4);
in.read((char *)&height, 4);
_byteswap_uint64(width);
_byteswap_uint64(height);
output_json = true;
in.close();
}
the width should be 155 , but output 2600468480
the height should be 80, but output 1342177280
visual-c++ byte png c++17 endianness
asked Nov 22 '18 at 8:54
Clarence NgClarence Ng
105
add a comment |
Hello i have problem to read out the correct data of png dimesnion size
unsigned width = 0;
unsigned height = 0;
bool output_json = false;
std::ifstream in(filepath, std::ios_base::binary | std::ios_base::in);
if (in.is_open())
{
in.seekg(16, std::ios_base::cur);
in.read((char *)&width, 4);
in.read((char *)&height, 4);
_byteswap_uint64(width);
_byteswap_uint64(height);
output_json = true;
in.close();
}
the width should be 155 , but output 2600468480
the height should be 80, but output 1342177280
visual-c++ byte png c++17 endianness
asked Nov 22 '18 at 8:54
Clarence NgClarence Ng
105
add a comment |
Hello i have problem to read out the correct data of png dimesnion size
unsigned width = 0;
unsigned height = 0;
bool output_json = false;
std::ifstream in(filepath, std::ios_base::binary | std::ios_base::in);
if (in.is_open())
{
in.seekg(16, std::ios_base::cur);
in.read((char *)&width, 4);
in.read((char *)&height, 4);
_byteswap_uint64(width);
_byteswap_uint64(height);
output_json = true;
in.close();
}
the width should be 155 , but output 2600468480
the height should be 80, but output 1342177280
visual-c++ byte png c++17 endianness
asked Nov 22 '18 at 8:54
Clarence NgClarence Ng
105
Hello i have problem to read out the correct data of png dimesnion size
unsigned width = 0;
unsigned height = 0;
bool output_json = false;
std::ifstream in(filepath, std::ios_base::binary | std::ios_base::in);
if (in.is_open())
{
in.seekg(16, std::ios_base::cur);
in.read((char *)&width, 4);
in.read((char *)&height, 4);
_byteswap_uint64(width);
_byteswap_uint64(height);
output_json = true;
in.close();
}
the width should be 155 , but output 2600468480
the height should be 80, but output 1342177280
visual-c++ byte png c++17 endianness
visual-c++ byte png c++17 endianness
asked Nov 22 '18 at 8:54
Clarence NgClarence Ng
105
asked Nov 22 '18 at 8:54
Clarence NgClarence Ng
105
asked Nov 22 '18 at 8:54
Clarence NgClarence Ng
105
asked Nov 22 '18 at 8:54
Clarence NgClarence Ng
105
asked Nov 22 '18 at 8:54
Clarence NgClarence Ng
105
105
add a comment |
add a comment |
1 Answer
1
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votes
the width should be 155 , but output 2600468480 the height should be 80, but output 1342177280
There is a problem of endianess.
2600468480 is, in exadecimal form 9b000000; 155 is 9b.
So the order of the less significat / most significant bytes is switched.
Try swapping the bytes
unsigned w0;
in.read((char *)&w0, 4);
width = ((w0 >> 24) & 0xff) |
((w0 << 8) & 0xff0000) |
((w0 >> 8) & 0xff00) |
((w0 << 24) & 0xff000000);
answered Nov 22 '18 at 11:00
max66max66
36.9k74166
add a comment |
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1 Answer
1
active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
the width should be 155 , but output 2600468480 the height should be 80, but output 1342177280
There is a problem of endianess.
2600468480 is, in exadecimal form 9b000000; 155 is 9b.
So the order of the less significat / most significant bytes is switched.
Try swapping the bytes
unsigned w0;
in.read((char *)&w0, 4);
width = ((w0 >> 24) & 0xff) |
((w0 << 8) & 0xff0000) |
((w0 >> 8) & 0xff00) |
((w0 << 24) & 0xff000000);
answered Nov 22 '18 at 11:00
max66max66
36.9k74166
add a comment |
the width should be 155 , but output 2600468480 the height should be 80, but output 1342177280
There is a problem of endianess.
2600468480 is, in exadecimal form 9b000000; 155 is 9b.
So the order of the less significat / most significant bytes is switched.
Try swapping the bytes
unsigned w0;
in.read((char *)&w0, 4);
width = ((w0 >> 24) & 0xff) |
((w0 << 8) & 0xff0000) |
((w0 >> 8) & 0xff00) |
((w0 << 24) & 0xff000000);
answered Nov 22 '18 at 11:00
max66max66
36.9k74166
add a comment |
the width should be 155 , but output 2600468480 the height should be 80, but output 1342177280
There is a problem of endianess.
2600468480 is, in exadecimal form 9b000000; 155 is 9b.
So the order of the less significat / most significant bytes is switched.
Try swapping the bytes
unsigned w0;
in.read((char *)&w0, 4);
width = ((w0 >> 24) & 0xff) |
((w0 << 8) & 0xff0000) |
((w0 >> 8) & 0xff00) |
((w0 << 24) & 0xff000000);
answered Nov 22 '18 at 11:00
max66max66
36.9k74166
the width should be 155 , but output 2600468480 the height should be 80, but output 1342177280
There is a problem of endianess.
2600468480 is, in exadecimal form 9b000000; 155 is 9b.
So the order of the less significat / most significant bytes is switched.
Try swapping the bytes
unsigned w0;
in.read((char *)&w0, 4);
width = ((w0 >> 24) & 0xff) |
((w0 << 8) & 0xff0000) |
((w0 >> 8) & 0xff00) |
((w0 << 24) & 0xff000000);
answered Nov 22 '18 at 11:00
max66max66
36.9k74166
answered Nov 22 '18 at 11:00
max66max66
36.9k74166
answered Nov 22 '18 at 11:00
max66max66
36.9k74166
answered Nov 22 '18 at 11:00
max66max66
36.9k74166
36.9k74166
add a comment |
add a comment |
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