c++ allocating memory problem

Question

hi,

i'm having a weird problem with allocating memory in c++ i'm creating a buffer and read file content into it. problem is the allocating is incorrect and at the end of the printing there are weird chars... the content of the file is "Hello"... i'm sitting on it for hours... what can be the problem ? :(

void main()
{
 FILE *fp;
 char *buffer;
 long file_size;
 size_t result;

 fp = fopen("input.txt","r");
 if (fp == NULL) { fputs("File Error",stderr); exit(1); }

 //get file size
 fseek(fp, 0, SEEK_END);
 file_size = ftell(fp);
 rewind(fp);

 //allocate memory to contain the whole file size
 buffer = new char[file_size];

 if (buffer == NULL) { fputs("Cannot allocate memory space",stderr); exit(2); }

 //copy the file into the buffer
 result = fread(buffer, 1, file_size, fp);
 if (result != file_size) { fputs("Reading error",stderr); exit(3); }

 cout<<buffer;
 fclose(fp);
 delete buffer;
 }

Answer 1

You are not zero-terminating your buffer, so it's not a valid C/C++ string.

Try the following changes:

//allocate memory to contain the whole file size, plus one char for termination
buffer = new char[file_size + 1];

if (buffer == NULL) { fputs("Cannot allocate memory space",stderr); exit(2); }

//copy the file into the buffer
result = fread(buffer, 1, file_size, fp);
if (result != file_size) { fputs("Reading error",stderr); exit(3); }

// terminate buffer, so it becomes a valid string we can print

buffer[file_size] = '\0';    
cout<<buffer;

Answer 2

buffer must contain a NULL terminated string for your cout<<buffer output to make sense.

Answer 3

Allocate one more place for termination character. And put it at the end of your buffer. This will probably solve your problem.

buffer = new char[file_size + 1];
buffer[file_size] ='\0';

Answer 4

When you are in C++, what speaks against using C++?

see: http://www.cplusplus.com/doc/tutorial/files/

edit2: in response to Neil (the initial version printed an empty line 0):

int main () {
        std::ifstream i ("main.cpp");
        std::string str;
        for (int line=0; getline (i, str); ++line) {
                std::cout << line <<  ':' << str << '\n';
        }
}