Funciones y Especificadores de Formato en Programación en C

C Programming Input/Output Functions and Format Specifiers

When writing programs in C, interacting with users and displaying output is crucial. This interaction often involves reading from files, keyboards, or other devices and printing text strings, numbers, and other data types using various input/output functions and format specifiers. In this section, we will explore some of these important concepts.

Input/Output Functions

In C, there are several functions available for performing I/O operations. Here are three commonly used ones:

1. printf() - Used for formatted output. It takes one argument which must be a string containing printf directives such as '%c' for characters or '%d' for integers.

#include <stdio.h>
int main(){
    int x = 5;
    double y = 8.9;
    float z = 2.5f;
    printf("x = %d\n", x); // Outputs: x = 5
    printf("%lf\n", y + z); // Outputs: 11.4
}

2. scanf() - Designed for scanning input, it reads input stream until whitespace or newline character. For example, if you enter 'Hello World!', it results in two inputs, 'Hello' and 'World!'. However, it is prone to security vulnerabilities due to buffer overflow issues because it assumes that the user input does not exceed the size specified by the programmer and stops parsing after encountering whitespace. A safer alternative for accepting user-entered values without knowing their length upfront is the fgets() function.

#include <stdio.h>
int main(){
    char str;
    scanf("%s", str);
    printf("You entered: %s\n", str);
}
// Pseudo code for safer input handling:
char str[MAX_INPUT_LENGTH];
if( fgets(str, MAX_INPUT_LENGTH+1, stdin) != NULL ){
    int len = strlen(str)-1; // Remove trailing '\n'.
    ...
}

3. fputs() - A low-level routine designed specifically for copying string literals to the file descriptor passed as its first parameter. While similar to fprintf, fputs has fewer options: no support for variable arguments, limited precision control over floating point emission, no ability to specify field width.

While there are more I/O functions like fread() and fwrite() available, these three serve as core components for simple console applications where dealing with streams isn't necessary. They offer different levels of complexity and safety for specific tasks.

Format Specifiers

Format specifiers are placeholders within a format string that determine how any subsequent parameters are treated. These specifiers are used when calling printf and scanf. Some common format specifiers are:

• %d - Decimal integer
• %f - Double floating point number
• %s - String data type

For example, consider the following usage:

printf("%d\n", i);     // Prints the value of i followed by a line feed.
printf("%f\n", d);    // Prints the value of d rounded to six decimal places.
printf("%s\n", s);   // Prints the contents of the string pointed to by s.

Similarly, for scanf:

double d;
char s[128];
...
sscanf(buf, "%lf %s", &d, s);       // Convert the first %lf token into a double and store it in the address of d.
                                               // Convert the second %s token into a string and store it in s array.

These format specifiers can be combined to create complex formats, allowing you to print and parse complex combinations of characters, numbers, and strings.

In conclusion, understanding both input/output functions and format specifiers is essential when working with C programming, especially for creating interactive command-line tools or console UI interfaces.