CODEWITHSUNDEEP
cstring
jingo
jingo

Reputation: 1074

Trouble with strings in C

I'm newbie in C world and I have two probably stupid questions.

I'm reading about structures in C and here is where I stuck. Let say we have structure like this

typedef structs {
  char model[50];
  int yearOfManufacture;
  int price;
} Car;

Car Ford;
Ford.yearOfManufacture = 1997;
Ford.price = 3000;

//The line below gives me an error "Array type char[50] is not assignable
Ford.model = "Focus"

How to pass text into Ford.model in that case ?

My second question is also about strings. This code works fine

char model[50] = "Focus";
printf("Model is %s", model);

But this one doesn't

char model[50];
model = "Focus";

Can anyone explain why it doesn't work ?

Upvotes: 5

Views: 3293

Answers (5)

Matt
Matt

Reputation: 3760

You can assign a string during definition, but anywhere else you have to use a different method, like the strcpy() function:

char model[50];
strcpy(model, "Focus");

Upvotes: 0

Constantinius
Constantinius

Reputation: 35039

This (Ford.model = "Focus") is not possible. You have to copy the string into the array in the struct, best with strcpy:

strcpy(Ford.model, "Focus");

If your stdlib supports it, you should also consider an overflow safe version, e.g strncpy:

strncpy(Ford.model, "Focus", sizeof Ford.model);

At least I think its an extension function and not in the standard... I'm not sure.

Upvotes: 1

pmg
pmg

Reputation: 108968

There are two ways to "put values in objects":

  • with initialization, when the object is created
  • with assignment, after the object is created

Though the syntax is similar, they represent different concepts.

You can initialize an array, but you cannot assign to it.

Also there's a special construct to initialize char arrays based on string literals

char arr[] = "foobar";
char arr[] = {'f', 'o', 'o', 'b', 'a', 'r', '\0'};
int arr[] = {1, 2, 3, 4};
// ...

but, assignement must be done element by element

char arr[4];
arr[0] = arr[1] = arr[2] = 'X';
arr[3] = '\0';
int arr[4];
arr[0] = arr[1] = arr[2] = 42;
arr[3] = -1;

A "special" way to assign elements of a char arrays one-by-one with a single statement is to use the library function strcpy() with prototype in <string.h>

#include <string.h>
int main(void) {
    char arr[10];
    strcpy(arr, "foo"); // same as arr[0]='f'; arr[1]=arr[2]='o'; arr[3]='\0';
    return 0;
}

Upvotes: 4

cnicutar
cnicutar

Reputation: 182609

That's not how you copy strings in C. Try

strcpy(Ford.model, "Focus");

Alternatively (but with very different semantics):

typedef structs {
  char const *model;
  int yearOfManufacture;
  int price;
} Car;

model = "Focus";

These C FAQs explain more about the issue:

Upvotes: 5

David Heffernan
David Heffernan

Reputation: 612794

You can't assign to a character array with =, you can only initialize it.

When you write 

char model[50] = "Focus";

that is a initialization.

When you write

model = ...

that is an assignment. And, as I said, assignment to character arrays is not allowed.

You need to copy to the character array using strcpy(), e.g. strcpy(model, "Focus").

Upvotes: 0

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