C语言文件流

输入输出 c语言

初步认识

• 文件读写

• 输入流和输出流 input stream output stream

• buffer 缓冲区

• 输入流的数据首先被暂存到一个叫做缓冲区的内存区域

再探scanf_s

 #include <stdio.h>​int main(void) {// 1.数的输入int age;printf("输入你的年龄：");scanf_s("%d", &age);    // 不需要加buffer 数没有缓冲区的概念 printf("年龄：%d\n", age);​// 2.字符串的输入char name[50];​printf("输入你的名字：");scanf_s("%49s", name, 50);  //scanf_s("%s", name, (unsigned int)sizeof(name));printf("Hello,%s\n", name);​// 3.字符的输入char ch;​printf("输入字符：");scanf_s("%c", &ch, 1);printf("字符：%c", ch);​return 0;}​

scanf_s返回值

 #include <stdio.h>​int main(void) {int number;int result;​puts("输入一个整数：");​result = scanf_s("%d", &number);​if (result == 1) {printf("你输入了有效的整型值：%d", number);}else if (result == EOF) {// End of file 通常为 -1// 专门用来指示文件读取或输入操作已经达到了数据源的末尾// 在终端中如果要把输入的东西撤销掉可以用ctrl+cprintf("An error occurred or end of file was reached");return 1;   // 表示程序出现错误的结束输出}else {printf("Invalid input for integer.\n");return 1;}​return 0;}​

流(stream)

1. 文件流：磁盘 用于读取与写入在磁盘上的文件

2. 标准I/O流：

   stdin:默认连接到键盘，用于程序输入

   stdout:默认连接到控制台或者是屏幕，用于程序输入

   stderr:默认连接到控制台或者是屏幕，专门输出错误信息和警告，使得其能够被区分开来或者是重定向到不同的目的地

3. 管道流:用于进程之间的通信(IPC),允许一个进程输出成为另一个进程的输入

4. 内存流:允许你将流与内存缓冲区关联，使得你可以向内存中读写数据，就像操作文件一样

5. 网络流:套接字(Sockets)

6. 设备流:特殊文件或者是设备 打印机

C语言用FILE* stream来操作

fopen_s,fgetc,fgets,fclose,读取r模式

 #include <stdio.h>#include <inttypes.h>​int main(void) {​FILE* file_stream = NULL;   //c语言操作流要使用的​char buffer[256];   //创建缓冲区​// fopen()打开文件的函数// fopen_s()跟缓冲区相关的函数，微软提供了_s的函数 传递的参数FILE** _Stream(使用的流),char const* _FileName(文件名), char const* _Mode(模式)​//打开文件设定文件路径要读取的文件，指定文件的操作模式rfopen_s(&file_stream, "C:\\c_learning\\c_stream.txt", "r");     // \\是转义序列输出\   "r" read读​​//fgets(buffer, sizeof(buffer), file_stream); 从文件中读取一行​while (fgets(buffer, sizeof(buffer), file_stream) != NULL) //停止循环可以用!= NULL {printf("%s", buffer);}​fclose(file_stream);​return 0;}

文件路径不对，文件不存在， 文件出现了异常，文件没有权限访问如何处理？

引入头文件#include <stdlib.h> #include <errno.h>

对14行进行修改

 errno_t err = fopen_s(&file_stream, "C:\\c_learning\\c_stream.txt", "r");       ​if (err != 0 || file_stream == NULL) {perror("Error opening file");return EXIT_FAILURE;}

当我们将文件路径更改后不会终止程序的输出 会输出Error opening file: No such file or directory

 #include <stdio.h>#include <inttypes.h>#include <stdlib.h>#include <errno.h>​int main(void) {​FILE* file_stream = NULL;   //c语言操作流要使用的​char buffer[256];   //创建缓冲区​// fopen()打开文件的函数// fopen_s()跟缓冲区相关的函数，微软提供了_s的函数 传递的参数FILE** _Stream(使用的流),char const* _FileName(文件名), char const* _Mode(模式)​//打开文件设定文件路径要读取的文件，指定文件的操作模式rerrno_t err = fopen_s(&file_stream, "C:\\c_learning\\c_stream.txt", "r");       // \\是转义序列输出\   "r" read读​​​if (err != 0 || file_stream == NULL) {perror("Error opening file");return EXIT_FAILURE;}​​while (fgets(buffer, sizeof(buffer), file_stream) != NULL) //停止循环可以用!= NULL {printf("%s", buffer);}​int ch;​// fgetc一个一个字符去获取 返回的是ASCII while ((ch = fgetc(file_stream)) != EOF)    //!= EOF也可以让它持续读取{putchar(ch);}​fclose(file_stream);​return 0;}

结果只会输出一次文本内容，因为file_stream指针把内容读完了，循环读完了，指针指向最后了，再往下什么都没有

如何解决只读一次的问题？

使用rewind()函数

在32行int ch;前面加上

 memset(buffer, 0, sizeof(buffer));​rewind(file_stream);

fclose()的优化 涉及文件写入就要按照下面的写法规范

 if (fclose(file_stream) != 0){perror("Error closing file!");return EXIT_FAILURE;}

fputs、fputc、w模式

 #include <stdio.h>#include <stdlib.h>​int main(void) {​FILE* file_ptr = NULL;​errno_t err = fopen_s(&file_ptr, "C:\\c_learning\\c_stream.txt", "w");  //"w"写入空的文件，若里面有内容，则先前的内容全部销毁​if (err != 0 || file_ptr == NULL) {perror("Failed to open file");return EXIT_FAILURE;}​// fputc() fputs() fprintf_s() 用与写入fputc('H', file_ptr);fputc('i', file_ptr);fputc('\n', file_ptr);​fputs("This is a line written by fputs.\n", file_ptr);​fprintf_s(file_ptr, "Numbers:%d, %f, %s\n", 10, 3.14, "End of example");    //格式化写入​fclose(file_ptr);​puts("File 'txt' has been written successfully");return 0;}

ftell、fseek、rewind、r+

txt内容为上一节输入的内容

#include <stdio.h>
#include <stdlib.h>int main(void) {FILE* file_ptr = NULL;errno_t err = fopen_s(&file_ptr, "C:\\c_learning\\c_stream.txt", "r+");	//r+打开以便读取和写入，文件必须存在if (err != 0 || file_ptr == NULL) {perror("Failed to open file");return EXIT_FAILURE;}long position = ftell(file_ptr);printf("当前位置：%ld\n", position);		//0char buffer[100];if ((fgets(buffer, sizeof(buffer), file_ptr)) != NULL) {printf("从文件读取：%s", buffer);		//Hi//再次使用ftell获取新位置position = ftell(file_ptr);printf("读取后的新位置：%ld\n", position);	//4 0:H 1:i 2:\r 3\n	windows中\r\n构成换行，fgets会把转义字符一起获取}//使用fseek函数移动到指定位置fseek(file_ptr, 0, SEEK_SET);printf("使用fseek后移动到文件的开始位置，SEEK_SET宏定义 = 0：%ld\n", ftell(file_ptr));	//0//rewind 重置文件指针到开头rewind(file_ptr);printf("使用rewind函数直接移动到开始位置%ld\n", ftell(file_ptr));	//0//关闭文件fclose(file_ptr);return 0;
}

fscanf_s

从流中读取格式化数据

//文件内容
//Hello 1234 5.67 Z#include <stdio.h>
#include <stdlib.h>FILE* stream;int main(void)
{long l;float fp;char s[81];char c;errno_t err = fopen_s(&stream, "C:\\c_learning\\c_stream.txt", "r");if (err)printf_s("The file fscanf.out was not opened\n");else{if (fscanf_s(stream, "%80s", s, (unsigned)_countof(s)) != 1) {  //%s：这是用于读取字符串的格式说明符。它会从输入流里读取连续的非空白字符，直至遇到空白字符（像空格、制表符、换行符等）才会停止。80指最多读取 80 个字符到目标字符串里printf("读取字符串失败!\n");}if (fscanf_s(stream, "%ld", &l) != 1) {printf("读取ld失败\n");}if (fscanf_s(stream, "%f", &fp) != 1) {printf("读取f失败\n");}if (fscanf_s(stream, " %c", &c, 1) != 1) {  //不加空格就会读取浮点数后面那个空格，输出一个空格printf("读取c失败\n");}// Output data read:printf("%s\n", s);printf("%ld\n", l);printf("%f\n", fp);printf("%c\n", c);fclose(stream);}
}

fprintf

fprintf：格式化向文件里写入东西

//文件内容
//ID:1
//Name:Frank
//Temperature : 36.5
//Grade : A#include <stdio.h>
#include <stdlib.h>FILE* stream;int main(void)
{long l;float fp;char s[81];char c;errno_t err = fopen_s(&stream, "C:\\c_learning\\c_stream.txt", "w+");if (err != 0) {printf_s("无法打开文件进行写入操作\n");return EXIT_FAILURE;}int id = 1;float temperature = 36.5f;char name[] = "Frank";char grade = 'A';fprintf(stream, "ID:%d\n", id);fprintf(stream, "Name:%s\n", name);fprintf(stream, "Temperature:%.1f\n", temperature);fprintf(stream, "Grade:%c\n", grade);fclose(stream);printf("数据写入完成\n");return 0;}

ferror,feof,clearerr

ferror:错误检查 检查文件流是否有错误发生 有错误返回非零值，无错误返回0

feof:错误检查 检查文件的指针是否到达了文件的末尾 到达返回非零值 没到达返回0

clearerr:清除错误 清除与文件流相关的错误标志

 #include <stdio.h>#include <stdlib.h>​FILE* file_ptr;​int main(void){errno_t err = fopen_s(&file_ptr, "C:\\c_learning\\c_stream.txt", "r");if (err != 0) {printf_s("无法打开文件进行写入操作\n");return EXIT_FAILURE;}​char buffer[100];​while (fgets(buffer, sizeof(buffer), file_ptr)) {printf("%s", buffer);}​if (ferror(file_ptr)) {perror("读取文件时候发生了错误");clearerr(file_ptr);}​if (feof(file_ptr)) {printf("已经到达文件的末尾\n");}else {printf("文件未达到末尾，可能因为发生了错误");}​​fclose(file_ptr);​return 0;}

抽离读写函数

 #include <stdio.h>#include <stdlib.h>#include <string.h>#include <errno.h>​void read_config_safe(const char* filename);​int main(void){const char* file_name = "C:\\c_learning\\game_config.txt";​read_config_safe(file_name);​return 0;}void read_config_safe(const char* filename) {FILE* file_ptr = NULL;errno_t err = fopen_s(&file_ptr, filename, "r");​if (err != 0 ||file_ptr == NULL) {char error_msg[256];strerror_s(error_msg, sizeof(error_msg), errno);​fprintf(stderr, "Failed to open config file for reading:%s\n", error_msg);exit(EXIT_FAILURE);}​char buffer[256];while (fgets(buffer, sizeof(buffer), file_ptr) != NULL) {printf("%s", buffer);}​fclose(file_ptr);​}​

文本内容：

# Game Configuration File

GraphicsQuality = High FullScreen = true Resolution = 1920 * 1080 AudioVolume = 80 EnableShadows = true; MaxNPCs = 50 Language = English

a模式追加

"a":在文件末尾打开以进行写入(追加)，在新数据写入到文件之前不移除文件末尾(EOF)标记。如果文件不存在，则创建文件

 #include <stdio.h>#include <stdlib.h>#include <string.h>#include <errno.h>​void append_log_safe(const char* file_name, const char* message);int main(void){const char* log_name = "C:\\c_learning\\log.txt";​const char* str = "This is an appending text";​append_log_safe(log_name, str);​return 0;​//确保所有流关闭int numclosed = fcloseall();printf("Number of files closed by _fcloseall : % u\n", numclosed);}void append_log_safe(const char* file_name, const char* message) {FILE* file_ptr = NULL;errno_t err = fopen_s(&file_ptr, file_name, "a");​if (err != 0 || file_ptr == NULL) {char error_message[256];strerror_s(error_message, sizeof(error_message), errno);​fprintf(stderr, "Failed to open log file for appending：%s\n", error_message);exit(EXIT_FAILURE);​}printf("成功创建并追加！\n");​fprintf(file_ptr, "%s\n", message);​fclose(file_ptr);}​

w模式清空

结合上一节内容，使用w模式清空log的内容

 #include <stdio.h>#include <stdlib.h>#include <string.h>#include <errno.h>​void append_log_safe(const char* file_name, const char* message);void clear_log_file(const char* file_name);​int main(void){const char* log_file = "C:\\c_learning\\log.txt";​const char* str = "This is an appending text";​append_log_safe(log_file, str);​//使用w模式的函数清空文件clear_log_file(log_file);​return 0;​//确保所有流关闭int numclosed = fcloseall();printf("Number of files closed by _fcloseall : % u\n", numclosed);}void append_log_safe(const char* file_name, const char* message) {FILE* file_ptr = NULL;errno_t err = fopen_s(&file_ptr, file_name, "a");​if (err != 0 || file_ptr == NULL) {char error_message[256];strerror_s(error_message, sizeof(error_message), errno);​fprintf(stderr, "Failed to open log file for appending：%s\n", error_message);exit(EXIT_FAILURE);​}printf("成功创建并追加！\n");​fprintf(file_ptr, "%s\n", message);​fclose(file_ptr);}void clear_log_file(const char* file_name) {FILE* file_ptr = NULL;errno_t err = fopen_s(&file_ptr, file_name, "w");​if (err!= 0 || file_ptr == NULL) {char error_message[256];strerror_s(error_message,sizeof(error_message), errno);​fprintf(stderr, "Failed to open log file for clearing:%s\n", error_message);exit(EXIT_FAILURE);}printf("成功清除文件！\n");​//文件已经是w模式，不用多加其他内容，文件内容会直接清空fclose(file_ptr);​}​​

修改log r+

c语言中数据的更新用r+模式

r+：打开以便读取和写入，文件必须存在

 #include <stdio.h>#include <stdlib.h>#include <string.h>#include <errno.h>​#define BUFFER_SIZE 1000​void append_log_safe(const char* file_name, const char* message);errno_t update_log_record_s(const char* file_name, const char* search_str, const char* replace_str);int main(void){const char* log_file = "C:\\c_learning\\frank.log";​const char* search_str = "Memory usage exceeds 80% of available memory";​const char* replace_str = "[2023-02-14T12:36:00Z] [INFO] Memory usage is back to normal levels";​errno_t result = update_log_record_s(log_file, search_str, replace_str);​if (result != 0) {char error_msg[256];strerror_s(error_msg, sizeof(error_msg), result);fprintf(stderr,"An error occured:%s\n", error_msg);}else {printf("Record updated successfully");}​_fcloseall();return 0;​}void append_log_safe(const char* file_name, const char* message) {FILE* file_ptr = NULL;errno_t err = fopen_s(&file_ptr, file_name, "a");​if (err != 0 || file_ptr == NULL) {char error_message[256];strerror_s(error_message, sizeof(error_message), errno);​fprintf(stderr, "Failed to open log file for appending：%s\n", error_message);exit(EXIT_FAILURE);​}printf("成功创建并追加！\n");​fprintf(file_ptr, "%s\n", message);​fclose(file_ptr);}errno_t update_log_record_s(const char* file_name, const char* search_str, const char* replace_str) {//卫语句if (file_name == NULL || search_str == NULL || replace_str == NULL) {return EINVAL; //返回无效参数错误}​FILE* file_ptr = NULL;errno_t err = fopen_s(&file_ptr, file_name, "r+");if (err != 0 || file_ptr == NULL) {char error_msg[256];strerror_s(error_msg, sizeof(error_msg), errno);​fprintf(stderr,"Failed to open config file for reading:%s\n", error_msg);exit(EXIT_FAILURE);​}char buffer[BUFFER_SIZE];long position = 0;int found = 0;​while (fgets(buffer, BUFFER_SIZE, file_ptr) != NULL) {if (strstr(buffer, search_str)!= NULL) {found = 1;//ftell会保存当前位置 记录下来position = ftell(file_ptr) - (long)strlen(buffer) - 1; //减1以确保从行首开始替换break;   // 找到第一个匹配项之后，立刻停止}}​if (found) {fseek(file_ptr, position, SEEK_SET); //移动找到记录的位置​//计算替换文本和源文本的长度差异size_t replace_len = strlen(replace_str);size_t search_len = strlen(search_str);​if (replace_len > BUFFER_SIZE - 1 || search_len > BUFFER_SIZE - 1) {fclose(file_ptr);​return ERANGE;   //返回错误码，表示字符串长度超出范围}​//写入新记录，清除所在位置的行数据memset(buffer, ' ', strlen(buffer)- 1);  //用空格去填充，保持文件大小不变​buffer[strlen(buffer) - 1] = '\n';   //保留换行符​fseek(file_ptr, position, SEEK_SET); //重新回到标记行的开始​fputs(buffer, file_ptr); //彻底清除原来行的内容​fseek(file_ptr, position, SEEK_SET); //重新回到标记行的开始​int result = fputs(replace_str, file_ptr);   //写入替换的字符​if (result == EOF) {fclose(file_ptr);return errno;}}else {fclose(file_ptr);return ENOENT;   //返回未找到的匹配项}fclose(file_ptr);return 0;​}

fflush()函数（略过）

立刻将缓冲区的数据保存

多线程用

错误日志可以用

bin二进制文件的写入与读取 wb和rb模式

二进制写入：游戏设置保存

 #include <stdio.h>#include <stdlib.h>​typedef struct GameSettings {float volume;int resolution_x;int resolution_y;int difficulty;​} GameSettings;​void save_game_settings(const GameSettings* settings, const char* filename);​int main() {​// fread// fwrite// 读写二进制​// 创建实例GameSettings settings = {0.75, 1920, 1080, 2};save_game_settings(&settings, "C:\\c_learning\\game_settings.bin");return 0;}void save_game_settings(const GameSettings* settings, const char* filename) {FILE* file;errno_t err = fopen_s(&file, filename, "wb");   //wb 写入二进制if (err != 0 ||file == NULL) {perror("无法打开文件进行写入操作");return;}​fwrite(settings, sizeof(GameSettings), 1, file);fclose(file);​}​​​

二进制读取：游戏设置读取

 #include <stdio.h>#include <stdlib.h>​typedef struct GameSettings {float volume;int resolution_x;int resolution_y;int difficulty;​} GameSettings;​​void load_game_settings(GameSettings* settings, const char* filename);int main() {​// fread// fwrite// 读写二进制​GameSettings load_settings;​load_game_settings(&load_settings, "C:\\c_learning\\game_settings.bin");​printf("游戏设置已经加载\n");​printf("音量：%f\n分辨率:%dx%d\n难度：%d星\n", load_settings.volume,load_settings.resolution_x,load_settings.resolution_y,load_settings.difficulty);​​​​​​return 0;}​void load_game_settings(GameSettings* settings, const char* filename) {FILE* file;errno_t err= fopen_s(&file, filename, "rb");if (err!= 0||file==NULL) {perror("无法打开文件进行读取操作");return;}​fread(settings, sizeof(GameSettings), 1, file);​fclose(file);​}​

复制文件

 #include <stdio.h>#include <stdlib.h>​int main() {FILE* source_file, * target_file;​char source_path[] = "C:\\c_learning\\c_stream.txt";​char target_path[] = "C:\\c_learning\\copy_stream.txt";​char buffer[1024];​size_t byte_read;​errno_t err = fopen_s(&source_file, source_path, "rb");​if (err != 0 ||source_file == NULL) {perror("无法打开源文件");return EXIT_FAILURE;​}​err = fopen_s(&target_file, target_path, "wb");if (err!= 0 || target_file == NULL) {perror("无法打开目标文件");fclose(source_file);return EXIT_FAILURE;}​while ((byte_read = fread(buffer, 1, sizeof(buffer), source_file)) > 0) {fwrite(buffer, 1, byte_read, target_file);}​_fcloseall();​puts("文件复制完成");​​​​return 0;}