User input from console in C

Question

I am a complete beginner in C programming, so please have some patience with me. I am trying to input a file name from the user in the console and I want to print a helpful message that prompts the user to enter the filename he wants to open. But when I run this in the command prompt, the cursor waits for the input first and after I enter some text and hit Return, I see the helpful prompt that I wanted to print before the input. Here is the code snippet.

 char filename[40];
 fputs("enter the file name: ", stdout);
 fflush(stdout); 
 fgets(filename, sizeof(filename), stdin);

I can't see where I am going wrong with this. I would really appreciate if some one could explain why this happens.

Answer 1

This works for me with gcc version 4.2.1 (Based on Apple Inc. build 5658) (LLVM build 2336.11.00):

char path[100];

printf("Give a path: ");

// Max length of 99 characters; puts a null terminated string in path, thus 99 chars + null is the max
scanf("%99s", path);

printf("This is your path: %s\n", path);

On a *nix machine, in assembly, to read and write:

read:   mov $0x03, %rax # Syscall Read
        mov $0x00, %rbx # Stdin
        mov $Buff, %rcx # Address to read to
        mov $BuffLen, %rdx  # Bytes to read
        int $0x80           # Call

write:  mov $0x04, %rax # Syscall Write
        mov $0x01, %rbx # Stdout
        mov $Buff, %rcx # Address to write from
        mov $BuffLen, %rdx  # Bytes to write
        int $0x80           # Call

This is some Windows assembly I got from a teacher:

.386
.MODEL FLAT

ExitProcess PROTO NEAR32 stdcall, dwExitCode:DWORD

GetStdHandle PROTO NEAR32 stdcall, nStdHandle:DWORD

ReadFile PROTO NEAR32 stdcall, hFile:DWORD, lpBuffer:NEAR32, NumberOfCharsToRead:DWORD,
     lpNumberOfBytesRead:NEAR32, lpOverlapped:NEAR32

WriteFile PROTO NEAR32 stdcall, hFile:DWORD, lpBuffer:NEAR32, NumberOfCharsToWrite:DWORD,
     lpNumberOfBytesWritten:NEAR32, lpOverlapped:NEAR32

STD_INPUT  EQU -10
STD_OUTPUT EQU -11

cr  EQU 0dh
Lf  EQU 0ah

.STACK
.DATA

InMsg   BYTE    14 dup (?)
msgLng  DWORD   $ - InMsg ;
read    DWORD   ?
written DWORD   ?
hStdIn  DWORD   ?
hStdOut DWORD   ?

.CODE
_start:
        INVOKE GetStdHandle, STD_INPUT
        mov     hStdIn, eax
        INVOKE ReadFile, hStdIn, NEAR32 PTR InMsg, msgLng, NEAR32 PTR read, 0
    INVOKE GetStdHandle, STD_OUTPUT
    mov hStdOut, eax
        INVOKE WriteFile, hStdOut, NEAR32 PTR InMsg, msgLng, NEAR32 PTR written, 0
    INVOKE ExitProcess, 0

PUBLIC  _start
END

Answer 2

I do not see any issues with the code you have pasted, works fine with gcc. It must be something to do with the stdout not being flushed, which could be specific to the compiler you are using...