C语言文件操作完全指南：从基础到实践
C语言文件操作完全指南
1. 文件操作基础概念
C语言将文件视为一个字符(字节)序列，由一个个字符(字节)数据顺序组成。根据数据组织形式可分为：
- ASCII文件：以字符形式存储，便于阅读和编辑
- 二进制文件：以二进制形式存储，节省空间且处理效率高
标准文件操作包括：打开、关闭、读写、状态检查以及定位等。
2. 文件打开与关闭
2.1 文件打开函数
FILE *fopen(char *pname, char *mode);功能说明：
- 按照mode规定方式打开pname指定的文件
- 若文件不存在：
- 写模式(mode包含'w')：创建新文件
- 读模式(mode包含'r')：返回错误
参数说明：
pname：要打开的文件名字符串mode：文件处理方式字符串，常见模式：- "r"：只读
- "w"：只写(创建新文件或清空已有)
- "a"：追加
- "r+"：读写(文件必须存在)
- "w+"：读写(创建新文件或清空已有)
- "a+"：读写(追加模式)
返回值：
- 成功：返回文件指针
- 失败：返回NULL
示例：
FILE *fp; if((fp=fopen("test", "r")) == NULL) { printf("The file can not be opened.\n"); exit(1); }2.2 标准设备文件
C语言将输入输出设备视为文件：
- 标准输入(stdin)：键盘
- 标准输出(stdout)：屏幕
- 标准错误(stderr)：错误输出
程序启动时自动打开这三个文件。
2.3 文件关闭函数
int fclose(FILE *fp);功能说明：
- 关闭fp指向的文件
- 释放文件结构体变量
- 返回操作结果
参数说明：
fp：已打开文件的指针
返回值：
- 成功：0
- 失败：EOF
示例：
int n = fclose(fp);3. 文件读写操作
3.1 字符读写
3.1.1 读取字符
int fgetc(FILE *fp);示例：显示文件内容
#include <stdio.h> void main(int argc, char *argv[]) { int ch; FILE *fp; if(argc != 2) { printf("Error format,Usage: display filename1\n"); return; } if((fp=fopen(argv[1], "r")) == NULL) { printf("The file <%s> can not be opened.\n", argv[1]); return; } ch = fgetc(fp); while(ch != EOF) { putchar(ch); ch = fgetc(fp); } fclose(fp); }3.1.2 写入字符
int fputc(int ch, FILE *fp);示例：文件复制
#include <stdio.h> void main(int argc, char *argv[]) { int ch; FILE *in, *out; if(argc != 3) { printf("Error in format,Usage: copyfile filename1 filename2\n"); return; } if((in=fopen(argv[1], "r")) == NULL) { printf("The file <%s> can not be opened.\n", argv[1]); return; } if((out=fopen(argv[2], "w")) == NULL) { printf("The file %s can not be opened.\n", argv[2]); return; } ch = fgetc(in); while(ch != EOF) { fputc(ch, out); ch = fgetc(in); } fclose(in); fclose(out); }3.2 字符串读写
3.2.1 读取字符串
char *fgets(char *str, int n, FILE *fp);3.2.2 写入字符串
int fputs(char *str, FILE *fp);示例：文件内容附加
#include <stdio.h> #define SIZE 512 void main(int argc, char *argv[]) { char buffer[SIZE]; FILE *fp1, *fp2; if(argc != 3) { printf("Usage: linkfile filename1 filename2\n"); return; } if((fp1=fopen(argv[1], "a")) == NULL) { printf("The file %s can not be opened.\n", argv[1]); return; } if((fp2=fopen(argv[2], "r")) == NULL) { printf("The file %s can not be opened.\n", argv[2]); return; } while(fgets(buffer, SIZE, fp1) != NULL) printf("%s\n", buffer); while(fgets(buffer, SIZE, fp2) != NULL) fputs(buffer, fp1); fclose(fp1); fclose(fp2); }3.3 格式化读写
3.3.1 格式化写入
int fprintf(FILE *fp, char *format, arg_list);3.3.2 格式化读取
int fscanf(FILE *fp, char *format, arg_list);示例：学生信息存储
#include <stdio.h> void main() { char name[10]; int nAge, nClass; long number; FILE *fp; if((fp=fopen("student.txt", "w")) == NULL) { printf("The file %s can not be opened.\n", "student.txt"); return; } fscanf(stdin, "%s %d %d %ld", name, &nClass, &nAge, &number); fprintf(fp, "%s %5d %4d %8ld", name, nClass, nAge, number); fclose(fp); if((fp=fopen("student.txt", "r")) == NULL) { printf("The file %s can not be opened.\n", "student.txt"); return; } fscanf(fp, "%s %d %d %ld", name, &nClass, &nAge, &number); printf("name nClass nAge number\n"); fprintf(stdout, "%-10s%-8d%-6d%-8ld\n", name, nClass, nAge, number); fclose(fp); }3.4 二进制读写
3.4.1 二进制读取
int fread(void *buffer, unsigned size, unsigned count, FILE *fp);3.4.2 二进制写入
int fwrite(void *buffer, unsigned size, unsigned count, FILE *fp);示例：结构体文件操作
#include <stdio.h> #define SIZE 4 struct worker { int number; char name[20]; int age; }; void main() { struct worker wk; int n; FILE *in, *out; if((in=fopen("file1.txt", "rb")) == NULL) { printf("The file %s can not be opened.\n", "file1.txt"); return; } if((out=fopen("file2.txt", "wb")) == NULL) { printf("The file %s can not be opened.\n", "file2.txt"); return; } while(fread(&wk, sizeof(struct worker), 1, in) == 1) fwrite(&wk, sizeof(struct worker), 1, out); fclose(in); fclose(out); }4. 文件状态检查
4.1 文件结束检测
int feof(FILE *fp);4.2 错误检测
int ferror(FILE *fp);4.3 清除错误标志
void clearerr(FILE *fp);4.4 获取当前位置
long ftell(FILE *fp);示例：带错误处理的文件复制
#include <stdio.h> void main(int argc, char *argv[]) { FILE *in, *out; char ch; if(argc != 3) { printf("Usage: copyfile filename1 filename2\n"); return; } if((in=fopen(argv[1], "rb")) == NULL) { printf("The file %s can not be opened.\n", argv[1]); return; } if((out=fopen(argv[2], "wb")) == NULL) { printf("The file %s can not be opened.\n", argv[2]); return; } while(!feof(in)) { ch = fgetc(in); if(ferror(in)) { printf("read error!\n"); clearerr(in); } else { fputc(ch, out); if(ferror(out)) { printf("write error!\n"); clearerr(out); } } } fclose(in); fclose(out); }5. 文件定位
5.1 重置文件指针
void rewind(FILE *fp);5.2 随机定位
int fseek(FILE *fp, long offset, int base);base参数取值：
- SEEK_SET：文件开头
- SEEK_CUR：当前位置
- SEEK_END：文件末尾
示例：随机访问学生记录
#include <stdio.h> #include <string.h> struct std_type { int num; char name[20]; int age; char class; } stud; int cstufile() { int i; FILE *fp; if((fp=fopen("stufile", "wb")) == NULL) { printf("The file can't be opened for write.\n"); return 0; } for(i=1; i<=100; i++) { stud.num = i; strcpy(stud.name, "aaaa"); stud.age = 17; stud.class = '8'; fwrite(&stud, sizeof(struct std_type), 1, fp); } fclose(fp); return 1; } void main() { int n; FILE *fp; if(cstufile() == 0) return; if((fp=fopen("stufile", "rb")) == NULL) { printf("The file can not be opened.\n"); return; } for(n=0; n<100; n+=2) { fseek(fp, n*sizeof(struct std_type), SEEK_SET); fread(&stud, sizeof(struct std_type), 1, fp); printf("%10d%20s%10d%4c\n", stud.num, stud.name, stud.age, stud.class); } fclose(fp); }