Unable to read the entire file correctly using fseek() and fread()

I have a file with shader source which i want to read that looks like this:

#version 460 core
layout(location = 0) in vec2 pos;
layout(location = 1) in vec3 color;
layout(location = 0) out vec3 fragColor;

uniform float rand;
out gl_PerVertex
  vec4 gl_Position;
  float gl_PointSize;
  float gl_ClipDistance[];

void main()
    fragColor = color * rand;
    gl_Position = vec4(pos.x + 0.5 * gl_InstanceID, pos.y, 0, 1);

first i find out the size of my file:

fseek(m_file, 0L, SEEK_END);
size_t size = ftell(m_file);

This returns 366. The problem is that if i just copy+paste the file content into a R"()" string and get a strlen it returns 347.
After getting file size i try reading the whole file:

fseek(m_file, 0, SEEK_SET);
size_t count = fread(buffer, 1, size, m_file);

where buffer is allocated with 366 bytes. But fread returns 347 and feof(m_file) returns true. So as a result i get this:

(File explorer also shows that the file size is 366).

However, when i read the same file into a string using std::ifstream, everything works properly:

std::ifstream ifs(filename);
std::string content((std::istreambuf_iterator<char>(ifs)),
auto size = content.size();

and size is equal to 347.

string content after reading a file with std::ifstream

The question is: am i doing something wrong or Windows/fseek just show the file size wrongly?


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