How to open a file and read data in C language?

1 year ago
Emily Johnson
1 minute

In C language, you can open a file using the fopen function and read data using the fscanf or fgets function.

Here is an example:

#include <stdio.h>

int main() {
    FILE *file; // 文件指针
    char buffer[100]; // 用于存储读取的数据

    file = fopen("file.txt", "r"); // 打开名为file.txt的文件以读取数据
    if (file == NULL) { // 检查文件是否成功打开
        printf("无法打开文件\n");
        return 1;
    }

    // 使用fscanf函数读取文件中的数据
    // %s表示读取字符串，%d表示读取整数，%f表示读取浮点数等
    while (fscanf(file, "%s", buffer) != EOF) {
        printf("%s\n", buffer);
    }

    // 使用fgets函数逐行读取文件中的数据
    // fgets函数的第一个参数为用于存储读取数据的字符数组，第二个参数为字符数组的大小，第三个参数为文件指针
    // fgets函数会读取一行数据，包括换行符，并将其存储在字符数组中
    // 当读取到文件末尾时，fgets函数返回NULL
    while (fgets(buffer, sizeof(buffer), file) != NULL) {
        printf("%s", buffer);
    }

    fclose(file); // 关闭文件

    return 0;
}

In the above example, the fopen function opens a file named file.txt to read data, using “r” as the second parameter to indicate opening the file in read-only mode. If the file is successfully opened, the fopen function returns a file pointer, otherwise it returns NULL.

Using the fscanf function allows for reading data from a file in a specified format, whereas the fgets function can read data from a file line by line.

After reading the data from the file, it is necessary to use the fclose function to close the file and release resources.

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