Answer by Alex Lop. for How do I fix an error in a header file typedef struct (expected a ";")?

typedef struct __attribute__((__packed__)) _bitmap

This is the way to define a struct definition without zero paddings in GCC.To prevent zero padding in MVSC, use #pragma pack:

#pragma pack(push,1)typedef struct _bitmap{ //Error is here on _bitmap    uint8_t magicNumber[2];    uint32_t size;    uint8_t reserved[4];    uint32_t startOffset;    uint32_t headerSize;    uint32_t width;    uint32_t height;    uint16_t planes;    uint16_t depth;    uint32_t compression;    uint32_t imageSize;    uint32_t xPPM;    uint32_t yPPM;    uint32_t nUsedColors;    uint32_t nImportantColors;} _bitmap;#pragma pack(pop) 

As you can see here https://godbolt.org/z/Gr-Rsw it compiles just fine.

Note that disabling padding is important to get the exact structure you want (first 2 bytes which are "magic number" then 4 bytes of size, etc). In such case you can read first sizeof(_bitmap) bytes from the file and expect the layout be exactly as defined in the struct.

Without the #pragma pack, the size of such struct may very based on different architectures. For example here the size is 56 byte, that's because the compiler adds padding after magicNumber[2] to align it to 4 bytes while with the pack attribute it is 54 bytes (example).