Ubuntu – Compiler prints HelloWorld whereas Chat GPT says it should only print Hello

Below is the code I’m compiling:

#include <stdio.h>
void main()
{
    printf("Hello%cWorldn", 0);
}

Below is the compiler output:

HelloWorld

Bing Chat-GPT response:start

Below is the same output by Bing chat-gpt in creative mode

Copilot:
The output of printf("Hello%cWorldn", 0) will be:

Hello

The reason is that the %c format specifier expects a single character as an argument, but you provided 0 instead. This is equivalent to the null character ”, which marks the end of a string in C1. Therefore, the printf function will stop printing the string after encountering the null character, and ignore the rest of the characters.

To print the whole string as it is, you need to use the %s format specifier, which expects a string as an argument. For example:

printf("Hello%sWorldn", "");

This will print:

HelloWorld

Alternatively, you can escape the backslash character with another backslash, like this:

printf("Hello\0Worldn");

This will also print:

HelloWorld

You:
but when I compiled the above code it gave me output as HelloWorld

Copilot:
That is strange. The code you posted should give a warning and print only Hello. Are you sure you compiled the same code? Maybe you have a different version of the compiler or the standard library that handles the null character differently. Can you show me the exact command you used to compile and run the code? 😊

You:
I have used gcc main.c -o app to compile

Copilot:
I see. And how did you run the app? Did you use any command-line arguments or input redirection? 😊

You:
I ran the app using ./app command I did not use any command-line arguments or input redirection

Copilot:
I see. Well, I’m not sure why you got a different output than expected. According to the C standard, the behavior of printf with a null character argument is undefined1. This means that different compilers or platforms may handle it differently, and there is no guarantee of consistency or correctness. Maybe your compiler or platform has some special treatment for the null character, or maybe you encountered some memory corruption or other bug.

To avoid this kind of problem, I suggest you always use valid arguments for the printf function, and follow the rules of the format specifiers. You can find more information about the printf function and its format specifiers in this article2.

I hope this helps. If you have any other questions, feel free to ask me. 😊

1: warning: format string contains ‘’ within the string body [-Wformat] 2: printf in C – GeeksforGeeks

Bing Chat-GPT response:end

Please note GCC version:

coder@069e69391cf2:~/project/Rough/programs/3$ gcc -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/9/lto-wrapper
OFFLOAD_TARGET_NAMES=nvptx-none:hsa
OFFLOAD_TARGET_DEFAULT=1
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu 9.2.1-9ubuntu2' --with-bugurl=file:///usr/share/doc/gcc-9/README.Bugs --enable-languages=c,ada,c++,go,brig,d,fortran,objc,obj-c++,gm2 --prefix=/usr --with-gcc-major-version-only --program-suffix=-9 --program-prefix=x86_64-linux-gnu- --enable-shared --enable-linker-build-id --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix --libdir=/usr/lib --enable-nls --enable-bootstrap --enable-clocale=gnu --enable-libstdcxx-debug --enable-libstdcxx-time=yes --with-default-libstdcxx-abi=new --enable-gnu-unique-object --disable-vtable-verify --enable-plugin --enable-default-pie --with-system-zlib --with-target-system-zlib=auto --enable-multiarch --disable-werror --with-arch-32=i686 --with-abi=m64 --with-multilib-list=m32,m64,mx32 --enable-multilib --with-tune=generic --enable-offload-targets=nvptx-none,hsa --without-cuda-driver --enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=x86_64-linux-gnu
Thread model: posix
gcc version 9.2.1 20191008 (Ubuntu 9.2.1-9ubuntu2) 

• I wanted to learn, in printf("Hello%cWorldn", 0) here %c expects matching int argument.
• Hence I gave 0, this turns out to be NULL with respect to ASCII characters.

I need to know why there are two different outputs i.e. compiler prints HelloWorld & chat-gpt
says only Hello should be printed.

Please help to explain this behavior ?

Thanks.