opening files and use of fseek to get size of file - C++

Question

I am doing one program with c++ and this program should be a lexical analyser to make a compiler. Thus I have made the header "AnalisadorLexical.h" where I defines all the functions and all the other things as pointers to files..., the "AnalisadorLexical.cpp" where I defines the logical of the functions and the main.cpp.

At the main.cpp I ask to the user to enter the name of the file to analyse and the name of to write the result. This is done inside a loop while for that the user enter many files to analyse. When the user enter the name of font file and the name o the final file I use the function fopen twice to open the first file and to write on the second. After this I invoke the constructor to get the size of the first file to create a vector where I will store the tokens of the file. My problema is when I use the fseek to get the size of the file. The execution of the program failure and I don't know what to do.

Follows their code.

main.cpp:

`int main(){

char *c1, *c2; 
c1 = new char[30]; 
c2 = new char[30]; 

FILE *f1; 
FILE *f2; 

cout<<"Arquivo de entrada:"<<endl; 

while(cin>>c1){

    cin>>c2; 

    f1 = fopen(c1, "r"); 
    f2 = fopen(c2, "w"); 

    AnalisadorLexico al(f1, f2);
    al.analiseLexica(); 
    fclose(f1); 
    fclose(f2); 
} 

return 0; }`

AnalisadorLexico.cpp - the constructor:

` AnalisadorLexico::AnalisadorLexico(FILE* f1, FILE* f2){

//Aloca os arquivos 
fp = f1;//arquivo sendo lido (de entrada)
fs = f2;//arquivo de saída

//tamanho do arquivo 
fseek(fp, 0L, SEEK_END);

tk_Size = ftell(fp);

//vetor de tokens 
tk_vet = new token[tk_Size];

//inicializa com 0
tk_count = 0;

monta_tabelaPR();
montaSb_vet();

}(...) `

AnalisadorLexico.h - the definition of constructor

` (...)

public:

//Construtor de classe 

AnalisadorLexico(FILE *f1, FILE *f2);

(...) `

Thank for your help guys.

Answer 1

You need to check the return value of fopen. If there's an error, you need to do something sane about it. Also, why aren't c1 and c2 std::strings?

Answer 2

I wouldn't bother trying to find the size of the file. However, I also wouldn't stick it into manually allocated memory. Instead, I would just read it into a std::vector<char> and get on with the work I'd actually have to do:

std::vector<char> v;
{
    std::ifstream in(c1);
    if (!in) {
        throw std::runtime_error("failed to open '" + std::string(c1) "' for reading");
    }
    v.insert(std::istreambuf_iterator<char>(in), std::istreambuf_iterator<char>());
}