從檔案中讀取行

stdio.h 標頭定義了 fgets() 功能。此函式從流中讀取一行並將其儲存在指定的字串中。當讀取 n - 1 字元，讀取換行符（'\n'）或到達檔案結尾（EOF）時，該函式停止從流中讀取文字。

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

#define MAX_LINE_LENGTH 80

int main(int argc, char **argv)
{
    char *path;
    char line[MAX_LINE_LENGTH] = {0};
    unsigned int line_count = 0;
    
    if (argc < 1)
        return EXIT_FAILURE;
    path = argv[1];
    
    /* Open file */
    FILE *file = fopen(path, "r");
    
    if (!file)
    {
        perror(path);
        return EXIT_FAILURE;
    }
    
    /* Get each line until there are none left */
    while (fgets(line, MAX_LINE_LENGTH, file))
    {
        /* Print each line */
        printf("line[%06d]: %s", ++line_count, line);
        
        /* Add a trailing newline to lines that don't already have one */
        if (line[strlen(line) - 1] != '\n')
            printf("\n");
    }
    
    /* Close file */
    if (fclose(file))
    {
        return EXIT_FAILURE;
        perror(path);
    }
}

使用引數呼叫程式，該引數是包含以下文字的檔案的路徑：

This is a file
  which has
multiple lines
    with various indentation,
blank lines

a really long line to show that the line will be counted as two lines if the length of a line is too long to fit in the buffer it has been given,
  and punctuation at the end of the lines.

將導致以下輸出：

line[000001]: This is a file
line[000002]:   which has
line[000003]: multiple lines
line[000004]:     with various indentation,
line[000005]: blank lines
line[000006]: 
line[000007]: 
line[000008]: 
line[000009]: a really long line to show that the line will be counted as two lines if the le
line[000010]: ngth of a line is too long to fit in the buffer it has been given,
line[000011]:  and punctuation at the end of the lines.
line[000012]: 

這個非常簡單的例子允許固定的最大線長度，這樣較長的線將有效地計為兩條線。fgets() 函式要求呼叫程式碼提供用作讀取行的目標的記憶體。

POSIX 使 getline() 功能可用，而是在內部分配記憶體以根據需要擴充套件任何長度的行（只要有足夠的記憶體）。