c - Warning for struct padding in Clang -

i created following structure:

typedef struct  s_fct_printf {   char          flag;   void          (*fct)(void*); }               t_fct_printf;  static const t_fct_printf       flags[] = {   { 's', my_putstr_printf },   //[...]   { 'b', display_base_2 }, }; 

but when compile clang -weverything, have following warning:

warning: padding struct 'struct s_fct_printf' 7 bytes       align 'fct' [-wpadded] 

i found following solution :

typedef struct  s_fct_printf {   char          flag;   void          (*fct)(void*);   char          pad[7]; }               t_fct_printf; 

but it's not solving problem:

warning: missing field 'pad' initializer [-wmissing-field-initializers]     { 'b', display_base_2 }, warning: padding struct 'struct s_fct_printf' 7 bytes       align 'fct' [-wpadded] 

so tried that:

typedef struct  s_fct_printf {   char          flag;   char          pad[7];   void          (*fct)(void*); }               t_fct_printf; 

but got following errors:

warning: incompatible pointer integer conversion initializing 'char'       expression of type 'void (void *)' [-wint-conversion]     { 'b', display_base_2 }, warning: suggest braces around initialization of subobject       [-wmissing-braces]     { 'b', display_base_2 }, warning: missing field 'fct' initializer [-wmissing-field-initializers]     { 'b', display_base_2 }, error: initializer element not compile-time constant     { 's', my_putstr_printf }, 

the last solution found that, have read it's not optimized since compilator not packaging variables anymore.

typedef struct __atribute__((__packed__))       s_fct_printf {   char          flag;   void          (*fct)(void*); }                                               t_fct_printf; 

is there solution?

typedef struct  s_fct_printf {   char          flag;   char          pad[7];   void          (*fct)(void*); }               t_fct_printf; 

is taking care of padding issue. however, you'll have change way initialize array.

use

static const t_fct_printf       flags[] = {   { 's', "", my_putstr_printf },   { 'b', "", display_base_2 }, }; 

otherwise, compiler tries initialize member pad my_putstr_printf, not want.

update

you can avoid hard coded number 7 size of pad using:

typedef struct  s_fct_printf {   char          flag;   char          pad[sizeof(void(*)(void))-1];   void          (*fct)(void*); }               t_fct_printf; 

thanks due @weathervane suggestion.