C: How can I know what header do I need for the functions I am using?

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Example program in C (without headers):

int main()
{
printf("\nHello World\n");
}

How can I know what include header (example: #include <stdio.h>) should I prepend?

Considering that you might not be able to search online (which would be the obvious choice most of the time I guess) and that you are on a linux machine you could also search for it in the man pages. To search inside the man pages you can use man -k {search term}

For example printf

$ man -k printf 
asprintf (3)         - print to allocated string
dprintf (3)          - formatted output conversion
fprintf (3)          - formatted output conversion
fwprintf (3)         - formatted wide-character output conversion
printf (1)           - format and print data
printf (3)           - formatted output conversion
snprintf (3)         - formatted output conversion
sprintf (3)          - formatted output conversion
swprintf (3)         - formatted wide-character output conversion
vasprintf (3)        - print to allocated string
vdprintf (3)         - formatted output conversion
vfprintf (3)         - formatted output conversion
vfwprintf (3)        - formatted wide-character output conversion
vprintf (3)          - formatted output conversion
vsnprintf (3)        - formatted output conversion
vsprintf (3)         - formatted output conversion
vswprintf (3)        - formatted wide-character output conversion
vwprintf (3)         - formatted wide-character output conversion
wprintf (3)          - formatted wide-character output conversion
XtAsprintf (3)       - memory management functions

$ man 3 printf
PRINTF(3)                                                                                  Linux Programmer's Manual                                                                                 PRINTF(3)

NAME
       printf, fprintf, dprintf, sprintf, snprintf, vprintf, vfprintf, vdprintf, vsprintf, vsnprintf - formatted output conversion

SYNOPSIS
       #include <stdio.h>

       int printf(const char *format, ...);
       int fprintf(FILE *stream, const char *format, ...);
...

How to determine which include header file a function comes from , The compiler doesn't need to know where it's coming from. coding practice to list the functions you will be using that are associated with each header: For instance, when I am writing .h files of my own and want to include the minimal cat t.c #include <stdio.h> int main(int argc, char* argv[]) { return 0; }. Using option (b) is a good practice and a good programmer always uses functions while writing code in C. Why we need functions in C. Functions are used because of following reasons – a) To improve the readability of code. b) Improves the reusability of the code, same function can be used in any program rather than writing the same code from

As has been mentioned in comments, you can use the search feature on https://en.cppreference.com/w/c/header.

Just make sure you select the C version of the function.

And the header you need to include is listed at the top of the page.

How to write your own header file in C?, As we all know that files with .h extension are called header files in C. is need to include stdio.h in our C program to use function printf() in the program. any name but the extension should be .h indicating its a header file. I have browsed many answers to those asking similar, though more specific questions, those answers are very direct - for this function, you need to include this header and that c file, never mentioning how these header/.c files were identified in the first place.

Use this as reference C library reference, to your code to work use this

#include <stdio.h>

You should always declare your C functions in header files, Home � Who am I? Notepad � Subscribe to Feed; Follow me; Facebook � Google+ You should always declare your C functions in header files As you know, you may not declare functions in C before using them. The c99 and c11 standards have removed this feature, but, by default, the compiler only� The standard C library does lots of things; explore header files in /usr/include to find out what it can do for you. The #include string is a C preprocessor (cpp) directive that causes the inclusion of the referenced file, in its entirety, in the current file.

Header files (C++), We add an #include directive for "my_class.h" file in order to have the Also, many standard library headers do not have .h or any other file extension. In to know is that my_class is a class that has a public member function� So the general idea of using headers is that you can have a special file that automatically declares all the functions you need by just #including it. However, headers also have one more common use. Let's suppose that main.c uses functions from 50 different files. The top of main.c would look like:

How to mix C and C++, C++ FAQ, What do I need to know when mixing C and C++ code? C++?; How do I call a C++ function from C? How can I include a standard C header file in my C++ code ? Why do I feel like I'm “further from the machine” in C++ as opposed to C? Note that you cannot create actual variables of the type; for that to work, the compiler needs to know how big the structure actually is, which means you need the details from the header. Strictly speaking, if you don't know the tag name, that won't work. And likewise, if the structure doesn't have a tag, you can't do it either. And if it isn't

C - Header Files, A header file is a file with extension .h which contains C function declarations and idea to copy the content of a header file in the source files, especially if we have the compiler will see the same token stream as it would if program.c read. The reason C and C++ source files are seperated here is because it makes a difference in some compilers. In all likelyhood (since you're reading this on a C++ site), you'll be using C++ code, so refrain from using the .c extension. Also, files with header extensions might be ignored by the compiler if you try to compile them.

Comments
  • You might try looking at this reference
  • tutorialspoint.com/c_standard_library
  • Google is your friend. "In C, what include file is needed for the function printf"
  • @EvilTeach but how long until google crawls this page, decides it is a better match for the search phrase and starts to return this page as the top result?
  • @FeiXiang just saying that seeing "Just google it" can be frustrating because Google (eventually) ends up prioritizing StackOverflow links most of the time. So somewhere down the line the top link ends up being a StackOverflow post with the exact question I search but the answer tells me to "Just google it".
  • You linked a website for C++, which doesn't include many of the C99 or any of the C11 standard library headers
  • it is a C library do look closely
  • No it is not. It only includes a subset of the C standard library, which is not already included in the C++ standard library. en.cppreference.com/w/c/header has a better list