Stream (pointer to a file structure) in File handling giving strange values - c++

Question

i am trying to output a buffer to a file using visual c++.
my code for doing it is-
FILE *stream;
stream=fopen("C:\\Users\\sshekha\\Desktop\\z.txt","r");
//I also tried with "w" mode
//the differencein behavious on executing these two is that when it is in read mode it
//executes the else condition in the code below whereas in "w" mode it executes the "if"
// condition,
//moreover even if i change the path it don't execute the "else" condition-that means this path
//is effective to the code. and the another surprising thing is when i open the file manually
// and then run the code with "r" mode it still executes the "else" part (which it shouldn't
// because the file is already open.)
if( stream == 0 )
{
MessageBox(m_hwndPreview,L" the file is not opened ",L"BTN WND",MB_ICONINFORMATION);
}
else
{
MessageBox(m_hwndPreview,L" the file is opened ",L"BTN WND",MB_ICONINFORMATION);
int check=fputs (HtmlFileContents,stream);
fclose(stream);
return 0;
}
I tried to check the results using different mode in order to understand whats teh probem going on . when i debug it , i get the value of (in Read mode) :
stream = 0x000000005c5c76f0 { _ptr=0x0000000000000000 _cnt=0 _base=0x0000000000000000 ...}
I don't know it gib=ves bad pointer and even then it go to else part of the loop. Why ?
and in write mode
stream = 0x0000000000000000 {_ptr=??? _cnt=??? _base=??? ...}
So go to the if part of the loop.
Moreover my path is correct and i have enough permission to do the task I wish. But why does it give bad pointer ? Why have I these strange values of stream and what should I do to copy the content of my buffer HtmlFileContents in to z.txt ? Any ideas ?

Answer 1

You're opening the file in read-only mode: fopen("C:\\Users\\sshekha\\Desktop\\z.txt","r");. Here "r" says you only intend to read from file. To be able to write contents (i.e. fputs(...)), open the file in write mode like so: fopen("C:\Users\sshekha\Desktop\z.txt","w")(or"a"` if you want to append). For more information, read fopen documentation.
EDIT: I see that you've tried both read and write modes. You're code only shows read-mode and hence my assumption on the read-only problem. Let me do a bit more research and get back.
Please write the following code in your if statement:
perror("The following error occurred:");
if you don't have a console, use this to store the error string:
char* errorCause = strerror(errno); MessageBoxA(m_hwndPreview, errorCause, "BTN WND", MB_ICONINFORMATION);
and let us know what you see as the cause.
EDIT 2: Since you've mentioned that you're using Visual Studio 2010, are you running it as yourself? This stackoverflow answer shows that VS2010 has different options when debugging applications; https://stackoverflow.com/a/3704942/210634
NOTE: That feature is only available on 'Pro' versions.
Here's a working example: https://ideone.com/hVLgc4

Answer 2

If the file is "read only", opening with it with write permissions should fail.
to see if that is the case,under windows:
right click the file
press properties
at the bottom, see if "Read-only" attribute i marked with "v"
(uncheck it if you desire writing to the file)
refer to :
http://msdn.microsoft.com/en-us/library/aa365535(v=vs.85).aspx
on how to change file permissions from your code