C: user defined strings and files

[iWearKiltz]

hi guys,

you're all so smart so I'm back again to ask where I'm going wrong (cause i really don't know and I've searched the web and haven't found anything thus far)

 

so i've opened a pre-defined file using fopen_s. I need to open a user-defined string. will not work right now D:

 

check it out for me please ?

 

code (some of which is a template for later things):

//This program is made for the purpose of text file analysis and merging of text files//This program was first created 3/12/2014//Made by Laurence Potter LP379#include <stdio.h>#include <stdlib.h>#include <string.h>    int main(void) {errno_t err;FILE *file_in; char ccount[5000], address1[200], address2[200]; printf("Please enter in the address of the text file you wish to open.\nPlease remember to 'escape' your backslashes: \n ");gets_s(address1, 199);printf("\nPlease enter in a second address of the text file you wish to open.\nPlease remember to 'escape' your backslashes: \n ");gets_s(address2, 199);printf("\n..."); err = fopen_s(&file_in, address1, "r");if (err == 0){printf("The file '%s' was opened\n", address1);}else{printf("The file '%s' was not opened\n", address1);} if (file_in){err = fclose(file_in);if (err == 0){printf("The file '%s' was closed\n", address1);}else{printf("The file '%s' was not closed\n", address1);}return 0;}} 

[Guest]

please format that code to look nicer

 

at

err = fopen_s(&file_in, address1, "r");

there is no need for &

[iWearKiltz]

please format that code to look nicer

 

at

err = fopen_s(&file_in, address1, "r");

there is no need for &

I get this error when doing your amendment

[Guest]

lol I missed one thing. Why you have file_in parameter in there?

 

fopen(const char *filename, const char *mode)

 

source

[iWearKiltz]

lol I missed one thing. Why you have file_in parameter in there?

 

fopen(const char *filename, const char *mode)

 

source

microsoft being microsoft decided to make things complicated by introducing a 'safer' version of fopen (and scanf etc) by putting '_s' on the end of them. This changes the format of the arguments and generally makes less sense (or at least to me) in comparison to the standard fopen.

 

now there are ways to get around the _s bit, but as this is for a university assignment, I'm trying to avoid that due to the fact that i suspect that they want me to use the more 'secure' fopen variety...

 

thanks for your help though

[Guest]

microsoft being microsoft decided to make things complicated by introducing a 'safer' version of fopen (and scanf etc) by putting '_s' on the end of them. This changes the format of the arguments and generally makes less sense (or at least to me) in comparison to the standard fopen.

 

now there are ways to get around the _s bit, but as this is for a university assignment, I'm trying to avoid that due to the fact that i suspect that they want me to use the more 'secure' fopen variety...

 

thanks for your help though

oh thats other story. Its late here where I am so I oversaw that _s

[iWearKiltz]

This is still an unsolved issue for anyone reading

[reiderj8]

Maybe try to take out the escape \ from the input. I know that you need a \\ to get a \ in C. However, looking at the output, it looks like it is not working at expected due to the string prints out like "home\\Documents\\...".

My guess is that get_s may remove the need to use the escape \ due to the fact normal users would have no clue that they need to type \\.  

[Avratz]

Escaping is only needed for string literals. User input doesn't need to. In your original example, you had the file paths hardcoded, and thus needed to escape them.

 

The *_s functions are done that way, so the function can return a meaningful error value. It's safer in the sense that you are handed the error code directly rather than relying on a global error flag. See the section on return values here http://msdn.microsoft.com/en-us/library/z5hh6ee9.aspx

 

For standard fopen you have to make a call to perror() or check the value of errno to get more information on the error. A NULL file handle isn't very meaningful beyond the fact it failed. Sometimes it's useful to know why.

 

ex

 

#include <stdio.h>#include <string.h>intmain(void){    FILE* fp;    char fname[128];    fgets(fname, 128, stdin);    fname[strlen(fname) - 1] = '\0';    fp = fopen(fname, "r");    if(!fp)    {        char buf[256];        sprintf(buf, "Failed to open %s ", fname);        perror(buf);        return 0;    }    char fbuf[128];    fgets(fbuf, 128, fp);    puts(fbuf);    fclose(fp);    return 0;} 

 

 

 

Microsoft version

 

#include "stdafx.h"int _tmain(int argc, _TCHAR* argv[]){    FILE* fp;    char fname[128];    fgets(fname, 128, stdin);    fname[strlen(fname) - 1] = '\0';    errno_t err;    err = fopen_s(&fp, fname, "r");    if (err)    {        char buf[256];        strerror_s(buf, 256, err);                fprintf(stderr, "Failed to open %s : %s", fname, buf);        return 0;    }    char fbuf[128];    fgets(fbuf, 128, fp);    puts(fbuf);    fclose(fp);	return 0;} 

 

[iWearKiltz]

Escaping is only needed for string literals. User input doesn't need to. In your original example, you had the file paths hardcoded, and thus needed to escape them.

 

The *_s functions are done that way, so the function can return a meaningful error value. It's safer in the sense that you are handed the error code directly rather than relying on a global error flag. See the section on return values here http://msdn.microsoft.com/en-us/library/z5hh6ee9.aspx

 

For standard fopen you have to make a call to perror() or check the value of errno to get more information on the error. A NULL file handle isn't very meaningful beyond the fact it failed. Sometimes it's useful to know why.

 

ex

 

#include <stdio.h>#include <string.h>intmain(void){    FILE* fp;    char fname[128];    fgets(fname, 128, stdin);    fname[strlen(fname) - 1] = '\0';    fp = fopen(fname, "r");    if(!fp)    {        char buf[256];        sprintf(buf, "Failed to open %s ", fname);        perror(buf);        return 0;    }    char fbuf[128];    fgets(fbuf, 128, fp);    puts(fbuf);    fclose(fp);    return 0;} 

 

 

 

Microsoft version

 

#include "stdafx.h"int _tmain(int argc, _TCHAR* argv[]){    FILE* fp;    char fname[128];    fgets(fname, 128, stdin);    fname[strlen(fname) - 1] = '\0';    errno_t err;    err = fopen_s(&fp, fname, "r");    if (err)    {        char buf[256];        strerror_s(buf, 256, err);                fprintf(stderr, "Failed to open %s : %s", fname, buf);        return 0;    }    char fbuf[128];    fgets(fbuf, 128, fp);    puts(fbuf);    fclose(fp);	return 0;} 

 

 

a lot of this is using syntax's which i haven't learnt/seen before.. thanks for showing me these, but i don't think i can use these as this is a uni assignment, so i can only really use what they've taught me... (though they haven't ever shown me how to put a string into a fopen_s yet

 

 

 

 

Maybe try to take out the escape \ from the input. I know that you need a \\ to get a \ in C. However, looking at the output, it looks like it is not working at expected due to the string prints out like "home\\Documents\\...".

My guess is that get_s may remove the need to use the escape \ due to the fact normal users would have no clue that they need to type \\.  

 

 

 

hmm, still not doing it

 

 

 

both screenshots show that a static address will show up the file as opened, but a user defined won't work... 

Edited December 4, 2014 by iWearKiltz

[Avratz]

Take address1 out of quotes in your fopen_s call. You're trying to open a file called "address1", not what you entered.

 

fopen_s(&file_in, address1, "r");

[iWearKiltz]

Take address1 out of quotes in your fopen_s call. You're trying to open a file called "address1", not what you entered.

 

fopen_s(&file_in, address1, "r");

me and you should become friends... or something similar

 

you've solved two of my problems now... have you done a c programming course/module?