Clanguagefileoperationtutorial

LearningClanguagefile 打开 and 关闭, 文本file and 二进制file 读写operation, file位置指针 operation

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1. fileoperationoverview

1.1 what is file

file is store in out 部store设备 (such as硬盘, U盘etc.) on 一组相关data collection. in Clanguagein, file可以分 for 两种class型:

  • 文本file: 以字符形式storedata, 每个字符 for 应一个ASCII码值, 适合store可阅读 文本data.
  • 二进制file: 以二进制形式storedata, 直接storedata 二进制表示, 适合storegraph像, 音频, 视频etc.非文本data, 以及需要 high 效store 数值data.

1.2 file指针

in Clanguagein, fileoperation is throughfile指针来for . file指针 is a 指向FILEclass型structure 指针, FILEstructure定义 in stdio.h头filein, package含了file 相关information, such asfile 位置指针, file 打开模式etc.. 

// 声明file指针
FILE *fp;

2. file 打开 and 关闭

2.1 file 打开

usingfopenfunction打开file, 该function 原型such as under : 

FILE *fopen(const char *filename, const char *mode);

其in:

  • filename: 要打开 file path and 名称.
  • mode: file 打开模式, 指定了file operation方式.
  • return value: 成功打开file时, 返回指向该file file指针; 失败时, 返回NULL.

常用 file打开模式: 

"r"   - 只读模式, 打开一个已存 in  文本file
"w"   - 只写模式, creation一个 new  文本file, such as果file已存 in 则清空其 in 容
"a"   - 追加模式, 打开一个文本file,  in file末尾添加data, such as果file不存 in 则creation
"rb"  - 只读模式, 打开一个已存 in  二进制file
"wb"  - 只写模式, creation一个 new  二进制file, such as果file已存 in 则清空其 in 容
"ab"  - 追加模式, 打开一个二进制file,  in file末尾添加data, such as果file不存 in 则creation
"r+"  - 读写模式, 打开一个已存 in  文本file
"w+"  - 读写模式, creation一个 new  文本file, such as果file已存 in 则清空其 in 容
"a+"  - 读写模式, 打开一个文本file,  in file末尾添加data, such as果file不存 in 则creation
"rb+" - 读写模式, 打开一个已存 in  二进制file
"wb+" - 读写模式, creation一个 new  二进制file, such as果file已存 in 则清空其 in 容
"ab+" - 读写模式, 打开一个二进制file,  in file末尾添加data, such as果file不存 in 则creation

2.2 file 关闭

usingfclosefunction关闭file, 该function 原型such as under : 

int fclose(FILE *stream);

其in:

  • stream: 要关闭 file指针.
  • return value: 成功关闭file时, 返回0; 失败时, 返回EOF (-1) .

关闭file important 性:

  • 释放file指针占用 resource
  • 确保所 has 缓冲区 data被写入file
  • 防止file被other程序占用

2.3 example: 打开 and 关闭file

#include <stdio.h>

int main() {
    FILE *fp;
    
    // 打开file
    fp = fopen("test.txt", "w");
    
    // checkfile is 否成功打开
    if (fp == NULL) {
        printf("file打开失败\n");
        return 1;
    }
    
    printf("file打开成功\n");
    
    // 关闭file
    if (fclose(fp) == 0) {
        printf("file关闭成功\n");
    } else {
        printf("file关闭失败\n");
    }
    
    return 0;
}

3. 文本file 读写operation

3.1 写入文本file

常用 写入文本file function:

3.1.1 fprintffunction

int fprintf(FILE *stream, const char *format, ...);

and printffunctionclass似, 但 is 将输出写入 to 指定 filein. 

#include <stdio.h>

int main() {
    FILE *fp;
    int num = 100;
    float score = 95.5;
    char name[] = "张三";
    
    // 打开file
    fp = fopen("test.txt", "w");
    
    // checkfile is 否成功打开
    if (fp == NULL) {
        printf("file打开失败\n");
        return 1;
    }
    
    // 写入data
    fprintf(fp, "姓名: %s\n", name);
    fprintf(fp, "年龄: %d\n", num);
    fprintf(fp, "成绩: %.1f\n", score);
    
    // 关闭file
    fclose(fp);
    
    printf("data写入成功\n");
    
    return 0;
}

3.1.2 fputsfunction

int fputs(const char *s, FILE *stream);

将string写入 to 指定 filein. 

#include <stdio.h>

int main() {
    FILE *fp;
    char str[] = "Hello, World!";
    
    // 打开file
    fp = fopen("test.txt", "w");
    
    // checkfile is 否成功打开
    if (fp == NULL) {
        printf("file打开失败\n");
        return 1;
    }
    
    // 写入string
    fputs(str, fp);
    fputs("\n", fp);  // 写入换行符
    fputs("Welcome to C programming!", fp);
    
    // 关闭file
    fclose(fp);
    
    printf("string写入成功\n");
    
    return 0;
}

3.1.3 putcfunction

int putc(int c, FILE *stream);

将单个字符写入 to 指定 filein. 

#include <stdio.h>

int main() {
    FILE *fp;
    char ch;
    
    // 打开file
    fp = fopen("test.txt", "w");
    
    // checkfile is 否成功打开
    if (fp == NULL) {
        printf("file打开失败\n");
        return 1;
    }
    
    // 写入字符
    for (ch = 'A'; ch <= 'Z'; ch++) {
        putc(ch, fp);
    }
    putc('\n', fp);  // 写入换行符
    
    // 关闭file
    fclose(fp);
    
    printf("字符写入成功\n");
    
    return 0;
}

3.2 读取文本file

常用 读取文本file function:

3.2.1 fscanffunction

int fscanf(FILE *stream, const char *format, ...);

and scanffunctionclass似, 但 is from 指定 filein读取输入. 

#include <stdio.h>

int main() {
    FILE *fp;
    char name[50];
    int age;
    float score;
    
    // 打开file
    fp = fopen("test.txt", "r");
    
    // checkfile is 否成功打开
    if (fp == NULL) {
        printf("file打开失败\n");
        return 1;
    }
    
    // 读取data
    fscanf(fp, "姓名: %s\n", name);
    fscanf(fp, "年龄: %d\n", &age);
    fscanf(fp, "成绩: %f\n", &score);
    
    // 输出读取 data
    printf("读取 data:\n");
    printf("姓名: %s\n", name);
    printf("年龄: %d\n", age);
    printf("成绩: %.1f\n", score);
    
    // 关闭file
    fclose(fp);
    
    return 0;
}

3.2.2 fgetsfunction

char *fgets(char *s, int size, FILE *stream);

from 指定 filein读取一行字符, store to 字符arrayin. 

#include <stdio.h>

int main() {
    FILE *fp;
    char buffer[100];
    
    // 打开file
    fp = fopen("test.txt", "r");
    
    // checkfile is 否成功打开
    if (fp == NULL) {
        printf("file打开失败\n");
        return 1;
    }
    
    // 读取file in 容
    printf("file in 容:\n");
    while (fgets(buffer, sizeof(buffer), fp) != NULL) {
        printf("%s", buffer);
    }
    
    // 关闭file
    fclose(fp);
    
    return 0;
}

3.2.3 getcfunction

int getc(FILE *stream);

from 指定 filein读取单个字符. 

#include <stdio.h>

int main() {
    FILE *fp;
    int ch;
    
    // 打开file
    fp = fopen("test.txt", "r");
    
    // checkfile is 否成功打开
    if (fp == NULL) {
        printf("file打开失败\n");
        return 1;
    }
    
    // 读取file in 容
    printf("file in 容:\n");
    while ((ch = getc(fp)) != EOF) {
        putchar(ch);
    }
    
    // 关闭file
    fclose(fp);
    
    return 0;
}

4. 二进制file 读写operation

4.1 写入二进制file

usingfwritefunction写入二进制file: 

size_t fwrite(const void *ptr, size_t size, size_t count, FILE *stream);

其in:

  • ptr: 指向要写入data memory地址.
  • size: 每个data项 big small (以字节 for 单位) .
  • count: 要写入 data项 数量.
  • stream: file指针.
  • return value: 成功写入 data项 数量. 
#include <stdio.h>

int main() {
    FILE *fp;
    int numbers[] = {10, 20, 30, 40, 50};
    int n = sizeof(numbers) / sizeof(numbers[0]);
    
    // 打开二进制file
    fp = fopen("data.bin", "wb");
    
    // checkfile is 否成功打开
    if (fp == NULL) {
        printf("file打开失败\n");
        return 1;
    }
    
    // 写入data
    size_t written = fwrite(numbers, sizeof(int), n, fp);
    printf("成功写入 %zu 个整数\n", written);
    
    // 关闭file
    fclose(fp);
    
    return 0;
}

4.2 读取二进制file

usingfreadfunction读取二进制file: 

size_t fread(void *ptr, size_t size, size_t count, FILE *stream);

其in:

  • ptr: 指向store读取data memory地址.
  • size: 每个data项 big small (以字节 for 单位) .
  • count: 要读取 data项 最 big 数量.
  • stream: file指针.
  • return value: 成功读取 data项 数量. 
#include <stdio.h>

int main() {
    FILE *fp;
    int numbers[5];
    int i;
    
    // 打开二进制file
    fp = fopen("data.bin", "rb");
    
    // checkfile is 否成功打开
    if (fp == NULL) {
        printf("file打开失败\n");
        return 1;
    }
    
    // 读取data
    size_t read = fread(numbers, sizeof(int), 5, fp);
    printf("成功读取 %zu 个整数\n", read);
    
    // 输出读取 data
    printf("读取 data: ");
    for (i = 0; i < read; i++) {
        printf("%d ", numbers[i]);
    }
    printf("\n");
    
    // 关闭file
    fclose(fp);
    
    return 0;
}

5. file位置指针 operation

5.1 file位置指针

file位置指针 is a 指向filein当 before 读写位置 指针. 当打开一个file时, file位置指针 初始位置取决于file 打开模式:

  • for 于"r", "rb"模式, file位置指针指向file 开头.
  • for 于"w", "wb"模式, file位置指针指向file 开头, 并且file被清空.
  • for 于"a", "ab"模式, file位置指针指向file 末尾.

5.2 file位置指针 operationfunction

5.2.1 ftellfunction

long ftell(FILE *stream);

获取当 before file位置指针 位置 (相 for 于file开头 偏移量, 以字节 for 单位) .

5.2.2 fseekfunction

int fseek(FILE *stream, long offset, int whence);

设置file位置指针 位置.

其in:

  • offset: 偏移量, 以字节 for 单位.
  • whence: 基准位置, 取值 for :
  • SEEK_SET: 以file开头 for 基准.
  • SEEK_CUR: 以当 before 位置 for 基准.
  • SEEK_END: 以file末尾 for 基准.

5.2.3 rewindfunction

void rewind(FILE *stream);

将file位置指针reset to file 开头, 相当于fseek(stream, 0, SEEK_SET). 

#include <stdio.h>

int main() {
    FILE *fp;
    char buffer[100];
    long position;
    
    // 打开file
    fp = fopen("test.txt", "r");
    
    // checkfile is 否成功打开
    if (fp == NULL) {
        printf("file打开失败\n");
        return 1;
    }
    
    // 读取第一行
    fgets(buffer, sizeof(buffer), fp);
    printf("第一行: %s", buffer);
    
    // 获取当 before 位置
    position = ftell(fp);
    printf("当 before 位置: %ld 字节\n", position);
    
    // 读取第二行
    fgets(buffer, sizeof(buffer), fp);
    printf("第二行: %s", buffer);
    
    // reset to file开头
    rewind(fp);
    printf("reset to file开头\n");
    
    // 再次读取第一行
    fgets(buffer, sizeof(buffer), fp);
    printf("再次读取第一行: %s", buffer);
    
    // usingfseek设置位置
    fseek(fp, position, SEEK_SET);
    printf("设置 to 之 before  位置\n");
    
    // 再次读取第二行
    fgets(buffer, sizeof(buffer), fp);
    printf("再次读取第二行: %s", buffer);
    
    // 关闭file
    fclose(fp);
    
    return 0;
}

6. fileoperation errorprocessing

6.1 error检测

in forfileoperation时, 应该始终checkfunction return value, 以检测可能发生 error:

  • for 于fopen, checkreturn value is 否 for NULL.
  • for 于fclose, checkreturn value is 否 for 0.
  • for 于fread, fwrite, checkreturn value is 否etc.于request 数量.
  • for 于fscanf, fgetsetc., checkreturn value is 否符合预期.

6.2 errorinformation

usingperrorfunction可以打印 and 当 before error码 for 应 errorinformation: 

#include <stdio.h>

int main() {
    FILE *fp;
    
    // 尝试打开一个不存 in  file
    fp = fopen("nonexistent.txt", "r");
    
    // checkfile is 否成功打开
    if (fp == NULL) {
        perror("file打开失败");
        return 1;
    }
    
    // 关闭file
    fclose(fp);
    
    return 0;
}

7. file delete and rename

7.1 deletefile

usingremovefunctiondeletefile: 

int remove(const char *filename);

成功deletefile时返回0, 失败时返回非零值.

7.2 renamefile

usingrenamefunctionrenamefile: 

int rename(const char *oldname, const char *newname);

成功renamefile时返回0, 失败时返回非零值. 

#include <stdio.h>

int main() {
    // renamefile
    if (rename("old.txt", "new.txt") == 0) {
        printf("filerename成功\n");
    } else {
        perror("filerename失败");
    }
    
    // deletefile
    if (remove("test.txt") == 0) {
        printf("filedelete成功\n");
    } else {
        perror("filedelete失败");
    }
    
    return 0;
}

实践case: 学生informationmanagementsystem (fileversion)

writing一个C程序, usingfilestore学生information, implementation添加学生information, 显示学生information, find学生information and 保存学生information to file functions.

requirementsanalysis

  • store many 个学生 information (姓名, 年龄, 成绩)
  • 添加学生information
  • 显示所 has 学生information
  • 根据姓名find学生information
  • 保存学生information to file
  • from file加载学生information

referencecode

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

// 声明学生structure体
typedef struct {
    char name[50];
    int age;
    float score;
} Student;

// function声明
void addStudent(Student students[], int *count);
void displayStudents(Student students[], int count);
void searchStudent(Student students[], int count);
void saveStudents(Student students[], int count, const char *filename);
void loadStudents(Student students[], int *count, const char *filename);

int main() {
    Student students[50];  // 最 many store50个学生
    int count = 0;         // 当 before 学生数量
    int choice;
    
    //  from file加载学生information
    loadStudents(students, &count, "students.dat");
    
    do {
        printf("\n学生informationmanagementsystem\n");
        printf("1. 添加学生information\n");
        printf("2. 显示所 has 学生information\n");
        printf("3. find学生information\n");
        printf("4. 保存学生information to file\n");
        printf("5. 退出\n");
        printf("请选择operation: ");
        scanf("%d", &choice);
        
        switch (choice) {
            case 1:
                addStudent(students, &count);
                break;
            case 2:
                displayStudents(students, count);
                break;
            case 3:
                searchStudent(students, count);
                break;
            case 4:
                saveStudents(students, count, "students.dat");
                break;
            case 5:
                // 退出 before 保存学生information
                saveStudents(students, count, "students.dat");
                printf("退出system\n");
                break;
            default:
                printf("无效选择, 请重 new 输入\n");
        }
    } while (choice != 5);
    
    return 0;
}

// 添加学生information
void addStudent(Student students[], int *count) {
    if (*count >= 50) {
        printf("学生数量已达 on 限\n");
        return;
    }
    
    printf("请输入学生information:\n");
    printf("姓名: ");
    scanf("%s", students[*count].name);
    printf("年龄: ");
    scanf("%d", &students[*count].age);
    printf("成绩: ");
    scanf("%f", &students[*count].score);
    
    (*count)++;
    printf("添加成功\n");
}

// 显示所 has 学生information
void displayStudents(Student students[], int count) {
    if (count == 0) {
        printf("暂无学生information\n");
        return;
    }
    
    printf("所 has 学生information:\n");
    printf("--------------------------------------------------\n");
    printf("姓名\t\t年龄\t成绩\n");
    printf("--------------------------------------------------\n");
    
    for (int i = 0; i < count; i++) {
        printf("%s\t\t%d\t%.1f\n", 
               students[i].name, students[i].age, students[i].score);
    }
    printf("--------------------------------------------------\n");
}

// 根据姓名find学生information
void searchStudent(Student students[], int count) {
    if (count == 0) {
        printf("暂无学生information\n");
        return;
    }
    
    char name[50];
    printf("请输入要find 学生姓名: ");
    scanf("%s", name);
    
    int found = 0;
    for (int i = 0; i < count; i++) {
        if (strcmp(students[i].name, name) == 0) {
            printf("找 to 学生information:\n");
            printf("姓名: %s\n", students[i].name);
            printf("年龄: %d\n", students[i].age);
            printf("成绩: %.1f\n", students[i].score);
            found = 1;
            break;
        }
    }
    
    if (!found) {
        printf("未找 to 该学生information\n");
    }
}

// 保存学生information to file
void saveStudents(Student students[], int count, const char *filename) {
    FILE *fp;
    
    // 打开file
    fp = fopen(filename, "wb");
    if (fp == NULL) {
        printf("file打开失败\n");
        return;
    }
    
    // 写入学生数量
    fwrite(&count, sizeof(int), 1, fp);
    
    // 写入学生information
    if (count > 0) {
        fwrite(students, sizeof(Student), count, fp);
    }
    
    // 关闭file
    fclose(fp);
    
    printf("学生information保存成功\n");
}

//  from file加载学生information
void loadStudents(Student students[], int *count, const char *filename) {
    FILE *fp;
    
    // 打开file
    fp = fopen(filename, "rb");
    if (fp == NULL) {
        printf("file打开失败, using空list\n");
        *count = 0;
        return;
    }
    
    // 读取学生数量
    fread(count, sizeof(int), 1, fp);
    
    // 读取学生information
    if (*count > 0) {
        fread(students, sizeof(Student), *count, fp);
    }
    
    // 关闭file
    fclose(fp);
    
    printf("学生information加载成功, 共 %d 个学生\n", *count);
}

互动练习

练习1: writing一个C程序, from 键盘输入一些文本, 将其写入 to 一个文本filein, 然 after 再 from 该filein读取 in 容并显示 in 屏幕 on .

提示: usingfgetsfunction from 键盘输入文本, usingfputsfunction写入file, 然 after usingfgetsfunction读取file in 容并显示.

练习2: writing一个C程序, statistics一个文本filein单词 数量.

提示: usingfscanffunction读取filein 单词, 直 to 遇 to EOF.

练习3: writing一个C程序, 将一个文本file in 容copy to 另一个文本filein.

提示: usinggetcfunction from sourcesfile读取字符, usingputcfunction将字符写入 to 目标filein.

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