C String Input and Output

There are many ways to read a string from the user. Each has some different behaviour.

scanf with %s

It reads only one word. It stops at the first space.

#include <stdio.h>

int main(void) {
    char name[30];

    scanf("%29s", name);
    printf("Hello, %s\n", name);
    return 0;
}

Output:

No & is needed with %s, because the array name is already an address. The number 29 limits the input, so it cannot overflow the 30 bytes array.

fgets: read a full line

fgets() reads a line with spaces. It is the safe way.

#include <stdio.h>
#include <string.h>

int main(void) {
    char name[30];

    fgets(name, sizeof(name), stdin);
    name[strcspn(name, "\n")] = '\0';   // remove the new line
    printf("Hello, %s\n", name);
    return 0;
}

Output:

fgets() also keeps the new line character (Enter key) in the string. The line with strcspn() removes it.

puts and printf

#include <stdio.h>

int main(void) {
    char msg[] = "Learning C";

    puts(msg);            // prints and adds a new line
    printf("%s\n", msg);
    return 0;
}

Output:

Do not use gets()

gets() cannot check the size of the array, so it can write outside the memory. It was removed from the C11 standard. Use fgets().

Next: C String Functions.

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