# <stdio.h>

**[<stdio.h>](https://en.cppreference.com/w/c/header/stdio)** provides buffered file and console I/O: `printf`, `scanf`, `fopen`, `fclose`, and stream operations. Use `snprintf` instead of `sprintf` to avoid buffer overflows; always check return values.

Compile with `-lm` if using math functions; I/O functions link with the C library automatically.

## Example

This example opens a file, writes formatted data, seeks, and reads it back.

```c
// compile: gcc -o studioexample studioexample.c
// run: ./studioexample
// description: write to file, seek to start, read back line by line

#include <stdio.h>

int main() {
    FILE* f = fopen("/tmp/stdio.txt", "w+");
    if (!f) { perror("fopen"); return 1; }
    
    fprintf(f, "line 1\n");
    fprintf(f, "line 2\n");
    fprintf(f, "line 3\n");
    
    rewind(f);
    
    char buf[64];
    while (fgets(buf, sizeof(buf), f))
        printf("read: %s", buf);
    
    fclose(f);
    return 0;
}
```

## Common functions

**File operations**:
- `fopen(path, mode)`: open file ("r", "w", "a", "r+", "rb", "wb", etc.)
- `fclose(file)`: close file (flushes and releases)
- `fflush(file)`: flush output buffer without closing
- `rewind(file)`: seek to beginning
- `fseek(file, offset, whence)`: seek to position (SEEK_SET, SEEK_CUR, SEEK_END)
- `ftell(file)`: current file position
- `remove(path)`: delete file
- `rename(old, new)`: rename file

**Formatted output** (to stdout, file, or buffer):
- `printf(fmt, ...)`: formatted output to stdout
- `fprintf(file, fmt, ...)`: formatted output to file
- `sprintf(buf, fmt, ...)`: formatted output to buffer (unsafe, use snprintf)
- `snprintf(buf, size, fmt, ...)`: formatted output to buffer (safe, no overflow)
- `vprintf(fmt, args)`, `vfprintf(f, fmt, args)`, `vsnprintf(buf, size, fmt, args)`: variadic versions

**Formatted input** (from stdin or file):
- `scanf(fmt, ...)`: formatted input from stdin
- `fscanf(file, fmt, ...)`: formatted input from file
- `sscanf(str, fmt, ...)`: formatted input from string
- `vscanf(fmt, args)`, `vfscanf(f, fmt, args)`, `vsscanf(s, fmt, args)`: variadic versions

**Text I/O** (line-oriented):
- `fgets(buf, size, file)`: read up to size-1 characters or newline
- `fputs(str, file)`: write string (without null terminator)
- `getchar()`: read character from stdin
- `putchar(c)`: write character to stdout
- `fgetc(file)`: read character from file
- `fputc(c, file)`: write character to file

**Binary I/O**:
- `fread(buf, size, count, file)`: read count objects of size bytes
- `fwrite(data, size, count, file)`: write count objects of size bytes

**Error handling**:
- `perror(msg)`: print system error message to stderr
- `ferror(file)`: check error flag
- `clearerr(file)`: clear error flag
- `eof(file)`: check end-of-file flag
- `fseek(file, offset, whence)`: seek to position
- `rewind(file)`: seek to start of file
- `perror(msg)`: print error message with errno