trying to declare a pointer to a typedef structure in C

converting some python code to C. 'just' want to declare a typedef structure and a pointer to it... this is segfaulting at printf( "byte order %p\n", info->byte_order);
How is this supposed to be done? please help. Trying to follow https://stackoverflow.com/questions/1543713/c-typedef-of-pointer-to-structure but I guess it is outdated.

#include <stdio.h>
#include <string.h>
#include <stdint.h>
#include <inttypes.h>
#include <Byteswap.h>

#define WFM_HEADER_SIZE 838

typedef struct WfmInfo{
  uint16_t byte_order;
//  char version[8];
  uint32_t imp_dim_count;
  uint32_t exp_dim_count;
  uint32_t record_type;
  uint32_t exp_dim_1_type;
  uint32_t time_base_1;
  uint32_t fastframe;
  uint32_t Frames;
  double   tstart;
  double   tscale;
  double   tfrac;
  double   tdatefrac;
  int32_t  tdate;
  uint32_t dformat;
  double   vscale;
  double   voffset;
  uint32_t pre_values;
  uint32_t post_values;
  uint32_t avilable_values;
  uint32_t dpre;
  uint32_t dpost;
  uint16_t bps;
  uint32_t code;
  uint32_t readbytes;
  uint32_t allbytes ;
  uint32_t samples;
  uint64_t curve_offset;
  uint32_t available_values;
} WfmInfo;

typedef WfmInfo* WfmInfo_ptr;

int testFuck(){
    WfmInfo_ptr info;
    printf( "info address %p\n", info);
    printf( "byte order %p\n", info->byte_order);
    cout<<"info declared"<<endl;
    return 0;
}

Here is a minimal example.

> want to declare a typedef structure and a pointer to it...

Compile like this:

gcc main.c -o main
./main

See output like this:

info address 0x7ff7be2e19b8
byte order 0x7ff7be2e19b8 = 3

// main.c
#include <stdio.h>
#include <inttypes.h>

typedef struct WfmInfo{
  uint16_t byte_order;
} WfmInfo;

typedef WfmInfo* WfmInfo_ptr;

int main(){
    // allocate the structure on the stack
    WfmInfo info = { 3 };
    // assign pointer the address on the stack
    WfmInfo_ptr info_ptr = &info;

    // display address using structure address
    printf( "info address %p\n", &info);

    // display address using pointer and display value using pointer to access elements of structure
    printf( "byte order %p = %d\n", info_ptr, info_ptr->byte_order);
    return 0;
}

Your typedefs are correct, WfmInfo_ptr is the type of a pointer to a WfmInfo structure.

The problem in the main function is you define such a pointer info but do not initialize it, so both printf calls have undefined behavior:

• printf( "info address %p\n", info); has undefined behavior because you %p expects a void * and you provide a WfmInfo *, which is not implicitly converted when passed to a vararg function
• info is uninitialized, so even if it was passed as (void *)info, the output would be meaningless.
• printf( "byte order %p\n", info->byte_order) has undefined behavior because you dereference an uninitialized pointer info.
• cout<<"info declared"<<endl; is C++ code, not C.

Note also that hiding pointers behind typedefs is considered confusing and error prone.

Defining info as WfmInfo *info; is quite readable and makes it obvious that info is a pointer that is not implicitly initialized (unlike a structure or class that might have a default constructor in C++).