C将值分配给结构可使用调试标志，但不能使用释放标志

Question

I'm working with C and OpenGL. I have a sprite struct, and a function to create a new sprite and set its' values. The function works correctly with debug linker flags, but when I compile it with release optimizations, some sprite values are set to 0. What am I doing wrong?

Minimal code example (EDITED):

#include <stdlib.h>
#include <stdio.h>

typedef struct {
    float x;
    float y;
    float z;
} position;

typedef struct {
    float r;
    float g;
    float b;
    float a;
} colorrgba8;

typedef struct {
    float u;
    float v;
} UV;

typedef struct {
    position pos;
    colorrgba8 color;
    UV uv;
} vertex;

typedef struct {
    float x, y, z;
    float width, height;

    vertex tr;
    vertex tl;
    vertex bl;
    vertex br;
} sprite;

vertex set_position(float x, float y, float z) {
    vertex ver;
    ver.pos.x = x;
    ver.pos.y = y;
    ver.pos.z = z;
    return ver;
}

vertex set_color(float r, float g, float b, float a) {
    vertex ver;
    ver.color.r = r;
    ver.color.g = g;
    ver.color.b = b;
    ver.color.a = a;
    return ver;
}

vertex set_uv(float u, float v) {
    vertex ver;
    ver.uv.u = u;
    ver.uv.v = v;
    return ver;
}

sprite*  sprite_new(float x, float y, float z, float width, float height) {
    sprite* s = malloc(sizeof(sprite));

    s->x = x;
    s->y = y;
    s->z = z;
    s->width = width;
    s->height = height;

    s->tr = set_position(x + width, y + height, z);
    s->tr = set_uv(1.0f, 1.0f);
    s->tr = set_color(1.0f, 1.0f, 1.0f, 1.0f);

    s->tl = set_position(x, y + height, z);
    s->tl = set_uv(0.0f, 1.0f);
    s->tl = set_color(1.0f, 1.0f, 1.0f, 1.0f);

    s->bl = set_position(x, y, z);
    s->bl = set_uv(0.0f, 0.0f);
    s->bl = set_color(1.0f, 1.0f, 1.0f, 1.0f);

    s->br = set_position(x + width, y, z);
    s->br = set_uv(1.0f, 0.0f);
    s->br = set_color(1.0f, 1.0f, 1.0f, 1.0f);


    return s;
}

I call the function like this:

sprite* s = sprite_new(100.0f, 100.0f, -100.0f, 100.0f, 100.0f);

printf("Top right vertex pos.x: %f | Bottom left vertex pos.z: %f\n", s->tr.pos.x, s->bl.pos.z);

Output with release flags: -O2

Top right vertex pos.x: 0.000000 | Bottom left vertex pos.z: 0.000000

Output with debug flags: -g -Wall -Wextra -Werror -Wwrite-strings -std=c99 -pedantic-errors

Top right vertex pos.x: 200.000000 | Bottom left vertex pos.z: -100.000000

Answer 1

You are not correctly initializing vertexes in various vertex functions.

In the first function that is called, set_position , you define a local vertex, and fully set member pos and its members with some values:

vertex set_position(float x, float y, float z) {
    vertex ver;
    ver.pos.x = x;
    ver.pos.y = y;
    ver.pos.z = z;
    return ver;
}

however you forget to set the other members, and then the struct is returned with some uninitialized members. Ie the struct from the function which is partially uninitialized is assigned to s->tr . Other members' values are indeterminate. Reading those members causes undefined behavior. All three functions suffer from this problem.

If you are not going to set the other elements, and the code can handle its default values then initialized the struct properly with default initializers for all its members:

vertex ver = { 0 } ;

The second problem is that the next two function overwrite the member tr of struct sprite. For every call, tr is overwritten. After the last call of function set_color , only members of tr.color are set and the rest are set to indeterminate values.

s->tr = set_position(x + width, y + height, z);
s->tr = set_uv(1.0f, 1.0f);
s->tr = set_color(1.0f, 1.0f, 1.0f, 1.0f);

The rest of the code replicates these same mistakes.