LANGUAGE » C » LIBRARIES
Stdio
Basic input & output
| Purpose | Function | Description |
|---|---|---|
| Input | scanf() | Read any kind of variable, syntax is similar to printf. Reading strings is tricky. |
| Input | fgets() | Read strings. New line included. |
| Output | printf() | Output to stdout in the format specified. |
| Output | puts() | Display string + a new line. |
c
#include <stdio.h>
int main(int argc, char *args[]) {
char name[20];
int age;
printf("Your name: ");
fgets(name, 20, stdin);
printf("Your age: ");
scanf("%d", &age);
printf("Hello %s, you are %d years old.\n", name, age);
return 0;
}File manipulation
Functions to manipulate content of files:
| File operation | Function |
|---|---|
| Open | fopen("path/file", "mode") |
| Seek | fseek(FILE*, offset, SEEK_SET | SEEK_END | SEEK_CUR) |
| Close | fclose(FILE*) |
| File type | Read function | Write function |
|---|---|---|
| Text | fscanf(FILE*, ...) | fprintf(FILE*, ...) |
| Binary | fread(data*, size, times, FILE*) | fwrite(data*, size, times, FILE*) |
When opening a file, there are 3 basic open modes:
| Mode | Use | Create file | Keep contents |
|---|---|---|---|
r rb | Reading | ✘ | ✔ |
w wb | Writing | ✔ | ✘ |
a ab | Appending | ✔ | ✔ |
You can also append a + (ex: wb+) so both read and write are available. The behavior of "Create file" and "Keep contents" is kept.
Example of reading and writing to text file.
c
#include <stdio.h>
int main() {
char filename[] = "salary.txt";
int salary;
FILE *file = fopen(filename, "r");
if (file) {
fscanf(file, "%d", &salary);
printf("Your salary was $%d per month.\n", salary);
fclose(file);
}
printf("Your new salary: ");
scanf("%d", &salary);
printf("I'll remember your new salary of $%d\nSee you later!", salary);
file = fopen(filename, "w");
fprintf(file, "%d", salary);
fclose(file);
return 0;
}Example of reading and writing to binary file.
c
#include <stdio.h>
#include <string.h>
int main() {
char filename[] = "username.save";
char user[50];
FILE *file = fopen(filename, "rb");
if (file) {
fread(user, sizeof(user), 1, file);
printf("Welcome back %s", user);
fclose(file);
}
printf("Your new user name: ");
fgets(user, 50, stdin);
printf("I'll remember your user name, %sSee you later!", user);
file = fopen(filename, "wb");
fwrite(user, strlen(user), 1, file);
fclose(file);
return 0;
}