code do not read text from file c++

Question

Microsoft Visual Studio 2017 C++

Problem is that code do not read text that is in the file MVS point by red wave test.txt and in dialog box is written: argument of type "const char" is incompatible with parameter of type char

File is in the project folder////

//

#include "stdafx.h"
#include "stdlib.h"
# include <fstream>
#include <stdio.h>


void HowManyWords(char FileName[]) {
  FILE*file = fopen(FileName, "rt");
//if (!file)return false;
int count = 0;
char str[100];
while (fgets(str, 100, file)) {
    for (int i = 0; str[i]; i++) {

        if (str[i] >= 'A'&&str[i] <= 'Z' || str[i] >= 'a'&&str[i] <= 'z') {
            if (str[i + 1] >= 'A'&&str[i + 1] <= 'Z' || str[i + 1] >= 'a'&&str[i + 1] <= 'z') {
            }
            else {
                count++;
            }
        }
    }
    printf("%s", str);
}
fclose(file);
printf("%i", count);
}

int main()
 {
HowManyWords("test.txt");

printf("\n");
system("pause");
return 0;
}

//111 words

Problem.

problem

Possible duplicate of [Why are string literals const?](https://stackoverflow.com/questions/14570993/why-are-string-literals-const) — Jim Lewis, Feb 27 '18 at 20:06
The only c++ in your code is `#include ` and it's commented out. — François Andrieux, Feb 27 '18 at 20:11
MSVC 2017 is a bit more standard compliant than its predecessors and providing a pointer to `const` data to a non-`const` pointer has long been verboten in standard C++ because it's dangerous as smurf. MSVC may have finally decided to close off this source of errors. — user4581301, Feb 27 '18 at 20:19
The compiler **is** telling you that you try to pass `const char` to a function expecting `char`. Do you think you can modify the function to actually expect `const char`? — Bo Persson, Feb 27 '18 at 20:19
BTW, you can reduce the number of comparisons by half, by using `std::tolower` or `std::toupper` — Thomas Matthews, Feb 27 '18 at 20:24
BTW, your algorithm is not counting "words" but some kind of letter combination. Words are usually separated by spaces or other punctuation (except maybe hyphenated words especially at line ends). — Thomas Matthews, Feb 27 '18 at 20:34
`void HowManyWords(char FileName[])` => `void HowManyWords(const char *FileName)` and for heavens sake, uncomment `//if (!file)return false;` otherwise you are racing off into *Undefined Behavior* if `fopen` fails. — David C. Rankin, Feb 28 '18 at 17:15

Thomas Matthews · Accepted Answer · 2018-02-28T16:20:51.393

1

One of the issues of your program is that your function take a pointer to Mutable, R/W character array:

void HowManyWords(char Filename[]);

In the main function, you are passing it a const char string. Text literals are constant.

If you are not changing the contents of Filename, pass it as "read-only":

void HowManyWords(char const * Filename)

Reading the type from right to left, this is a pointer to constant ("read only") char. The function is stating that it will not change the contents of Filename. Thus you can pass it a string literal.

For more information, search the internet for "c++ const correctness pointers".

Edit 1: simple example
Here is a simple working example showing the correct parameter syntax for your HowManyWords function:

#include <stdio.h>

void HowManyWords(const char Filename[])
{
    puts("Filename: ");
    puts(Filename);
    puts("\n");
}

int main()
{
    HowManyWords("test.txt");
    puts("\n");
    return 0;
}

Here is the compilation and output, using g++ on Cygwin, on Windows 7:

$ g++ -o main.exe main.cpp

$ ./main.exe
Filename:
test.txt





$

As I stated above, comment out your code in HowManyWords and get the parameter passing working correctly. Next, add a little bit of code; compile, test and repeat.

edited Feb 28 '18 at 16:20

answered Feb 27 '18 at 20:33

Thomas Matthews

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It still not working .I just want that it showed result in consol – Inex Feb 27 '18 at 20:50
Can you please send me a code that is working(fixed version of main)? – Inex Feb 27 '18 at 20:52
My answer should remove the compiler warning or error. As for why your program is not working correctly, step through with a debugger. – Thomas Matthews Feb 27 '18 at 20:52
If you are allergic to debuggers, insert some `printf` statements to display the values of variables. – Thomas Matthews Feb 27 '18 at 20:55
You could always comment all the code in your function, compile and test. Next, uncomment the next line. Compile and test. Repeat until you find the statements that are failing. – Thomas Matthews Feb 27 '18 at 20:56
Sorry, but I'm getting paid enough to use debuggers for other people. – Thomas Matthews Feb 27 '18 at 20:57
How can I debug if I even can not enter to compile it because error in HowManyWords("test.txt"); ? – Inex Feb 27 '18 at 21:04
@Inex: See my latest edit. If that is not working, you'll have open up your IDE, compile, and move to the right so I can see the *compiler or build error messages*. – Thomas Matthews Feb 28 '18 at 16:22

code do not read text from file c++

1 Answers1