using strcpy to store a string that has many variables

Question

I'm not sure how to word it, so the title may be unclear. Here's the line in question

strcpy (stringstore,"int1: %d\nint2: %d\nint3: %d\nint4: %d\nstring1: %s\nstring2: %s\n",int1,int2,int3,int4,string1,string2);

This is inside a for loop so the values of the ints and strings are changing. I want to store each string in stringstore. How would I be able to do this?

EDIT: Here is more code.

int id;
int year;
char title[30];
char director[30];
double price;
double length;
int i;
char stringstore[300];
FILE *outp;
outp= fopen("CurrentCatalog.txt","w");
for (i = 0;i<=*size;i++)
{
    id = entry[i].id;
    year = entry[i].year;
    strcpy(title,entry[i].title);
    strcpy(director,entry[i].director);
    price = entry[i].price;
    length = entry[i].length;
    fprintf(outp,"ID: %d\nTitle: %s\nDirector: %s\nYear: %d\nPrice: %.2f\nLength: %.2f\n",id,title,director,year,price,length);
}
fclose(outp);

Look it up. It's a standard C function and works like you try to use `strcpy` (your call won't compile). — mafso, Jul 22 '14 at 16:52
Have a look at the [C-wiki](http://stackoverflow.com/tags/c/info) for tutorial and manuals explaining all you need to know: http://stackoverflow.com/tags/c/info — Soren, Jul 22 '14 at 16:52

score 2 · Answer 1 · answered Jul 22 '14 at 17:02

2

Always prefer snprintf to convert any data's to string. prototypes for sprintf and snprintf

int sprintf(char *str, const char *format, ...);
int snprintf(char *str, size_t size, const char *format, ...);

Make the following change in your code

snprintf(stringstore,sizeof(stringstore),"int1: %d\nint2: %d\nint3: %d\nint4: %d\nstring1: %s\nstring2: %s\n",int1,int2,int3,int4,string1,string2);

answered Jul 22 '14 at 17:02

Sathish

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It's not a function in the libraries I have. I am not using C99. – Jul 22 '14 at 17:06

Valentin Mercier · Answer 2 · 2014-07-22T17:02:18.103

1

Yes you can do it. The function you are looking for is sprintf()not strcpy(). Its the same syntax.

sprintf(stringstore,"int1: %d\nint2: %d\nint3: %d\nint4: %d\nstring1: %s\nstring2: %s\n",int1,int2,int3,int4,string1,string2);

EDIT: as suggested by @chris a safer way to do it is to use snprintf()

char stringstore[500];
snprintf(stringstore, 500, "int1: %d\nint2: %d\nint3: %d\nint4: %d\nstring1: %s\nstring2: %s\n",int1,int2,int3,int4,string1,string2);

EDIT2 From the new code you posted above, I suggest you merge your sprintf and your fprintf

fprintf(outp,"ID: %d\nTitle: %s\nDirector: %s\nYear: %d\nPrice: %.2f\nLength: %.2f\n",id,title,director,year,price,length);

edited Jul 22 '14 at 17:02

answered Jul 22 '14 at 16:50

Valentin Mercier

5,256
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That should be `snprintf`. – chris Jul 22 '14 at 16:52
Okay, I did this but I get a different error-- The stack around stringstore is corrupted. How can I fix this? – Jul 22 '14 at 16:53
Depends on the input stringstore, but yeah. – Valentin Mercier Jul 22 '14 at 16:53
@realdealcs, before calling this function, make sure your stringstore is big enough. For instance declare it like `char stringstore[100];` – Valentin Mercier Jul 22 '14 at 16:55
@ValentinMercier Yeah i did and now my program crashes, but i dont get the error. – Jul 22 '14 at 16:56
@realdealcs Make sure stringstore is big enough to receive all the text. If the final outcome is bigger than 100 make your stringstore size bigger – Valentin Mercier Jul 22 '14 at 16:58
I made it 200, but it still crashes. I think the problem is from somewhere else. I will take another look at it. – Jul 22 '14 at 16:59
It is hard to see what goes wrong there. So instead of one line, show us more of your code. – Rudy Velthuis Jul 22 '14 at 17:00
Try with snprintf and pass 300 as second parameter between stringstore and the main string – Valentin Mercier Jul 22 '14 at 17:00
snprintf is undefined. What library is it in? – Jul 22 '14 at 17:02
It is in stdio. But only since C99. Make sur your compiler has C99 support enabled – Valentin Mercier Jul 22 '14 at 17:03
I don't have C99. And my assignment won't be graded using it either so I won't be able to use it. – Jul 22 '14 at 17:05
I tried it, and it still crashed my program. I will add the call. Maybe that is the problem. – Jul 22 '14 at 17:09
I added the entire function definition. – Jul 22 '14 at 17:11

ryyker · Answer 3 · 2014-07-22T22:48:13.507

Regarding ...using *strcpy()* to store a string that has many variables...

The short answer is, you don't. Use sprintf() (or one of it's variants) instead. (see below)

I want to store each string in stringstore. How would I be able to do this? If you want to store each new set of data, without loosing it in subsequent the iterations of the loop, You need to make stringstore an array of strings. i.e. create it with:

char **stringstore = 0;//will provide for an array of strings when memory is allocated

Then allocate memory for it.

Edit: (per your comment)

If you do not need to keep previous information, a single string (char array) of sufficient length will work:

#define MAX_LEN 280;//arbitrary size choice as you have not specified size in your code
char *stringstore = 0;  
stringstore = malloc(MAX_LEN +1);// +1 for null terminator

Then you can place information into stringstore like this:

sprintf(stringstore,"int1: %d\nint2: %d\nint3: %d\nint4: %d\nstring1: %s\nstring2: %s\n",int1,int2,int3,int4,string1,string2);

Using this method places memory for stringstore onto the heap as opposed to the stack, so you will need to free it when done using it.

free(stringstore);

Note:
There may be other questions you should be asking about your code, such as
after opening the text file, how do I read the data into my variables? .
(You open the text file, then enter the loop, but have
never read data from the file to populate the variables used in the loop.)

I don't want to store the previous. This is only a temporary holder of the string. — , Jul 22 '14 at 17:06

using strcpy to store a string that has many variables

3 Answers3