Unexpected Behavior with Variadic Functions and Structs in C - Incorrect Parameter Passing
I'm confused about I'm working on a project and hit a roadblock... I'm facing an issue with a variadic function that is supposed to accept different types of arguments, including a struct. The variadic function is designed to log information based on the parameters passed to it. However, when I attempt to pass a struct pointer, it seems to not work as expected, resulting in incorrect logging output. Here's the signature of my variadic function: ```c void log_info(const char *format, ...); ``` And I call it like this: ```c typedef struct { int id; char name[50]; } User; User user = {1, "Alice"}; log_info("User ID: %d, Name: %s", user.id, user.name); ``` Yet, when I try to log the struct directly: ```c log_info("User details: %s", &user); ``` I receive this warning during compilation: ``` wformat.c: In function ‘log_info’: wformat.c:12:9: warning: format ‘%s’ expects argument of type ‘char *’, but argument 2 has type ‘User *’ [-Wformat=] ``` This makes sense because I am trying to pass a pointer to a struct instead of a string. However, I expected to be able to handle this scenario. What’s the correct way to pass a struct to a variadic function in C? Should I create a custom format specifier or is there a more standard approach? I’ve tried passing the struct as a pointer and casting it in the function, but it still doesn’t seem to produce the desired output. Here’s what I attempted in my `log_info` implementation: ```c #include <stdio.h> #include <stdarg.h> void log_info(const char *format, ...) { va_list args; va_start(args, format); vprintf(format, args); va_end(args); } ``` I would appreciate guidance on how to correctly handle variadic arguments, especially when dealing with structs, to avoid such type mismatches. Any insights would be helpful! This is part of a larger application I'm building. How would you solve this? Hoping someone can shed some light on this.