王道c语言-文件操作

fopen fgetc fputc fwrite fread fgets fputs

//main.c
#include <stdio.h>
#include <string.h>

int main() {
    FILE *fp;
    int ret;

    //打开/创建文件
    fp = fopen("test.txt", "wb+");
    if (NULL == fp) {
        perror("fopen fail");//perror aim to find reason of error
        return -1; //程序退出码为-1，说r退出异常
    }

    /*
     * putc写操作
     */
    int i=fputc('a',fp); //写入成功返回写入字符，否则 EOF
    if(EOF == i){
        //如果提示 fputc error: Bad file descriptor，看是否读写权限有误
        perror("fputc error");
    }
    printf("putc = %c\n",i); //一般i=1

    /*
     * getc读操作
     */
    char c;
    long long pos;
    fseek(fp,-1,SEEK_CUR);
    pos= ftell(fp);       //获取位置指针距离文件开头的位置
    printf("after fseek pos=%ld\n",pos);
     while ( (c=fgetc(fp) ) != EOF){
        printf("%c",c);
    }
    printf("\nend of file\n");
    pos= ftell(fp);
    printf("after fgetc pos=%ld\n",pos);

    /*
     * fwrite fread 读写操作-字符串
     */
    char buf[20]="hello\nworld";
    ret = fwrite(buf,sizeof (char), strlen(buf),fp);
    printf("fwrite ret = %d\n",ret);
    fseek(fp,-strlen(buf),SEEK_CUR);
    memset(buf,0,sizeof (buf));
    printf("%buff= %s\n",buf);
    ret= fread(buf,sizeof (char),sizeof (buf),fp);
    printf("fread ret = %d\n",ret);
    pos= ftell(fp);
    printf("after fwrite pos=%ld\n",pos); //21

    /*
     * fwrite fread 读写操作-二进制数据-整数
     */
//    int num = 123456;
//    ret=fwrite(&num, sizeof(int), 1, fp);
//    printf("fwrite num ret = %d\n",ret); //1
//    fseek(fp,-sizeof(int),SEEK_CUR);
//    num=0;
//    ret = fread(&num, sizeof (int), 1, fp);
//    printf("fread num ret = %d\n",ret);  //1
//    printf("num = %d\n",num);  //123456
//    long long pos= ftell(fp);
//    printf("after fwrite pos=%ld\n",pos); //16
//
//    /*
//     * fgets puts 读写操作
//     *  fgets替换scanf: buf是字符串数组，fgets(buf,sizeof(buf),stdin);
//     *      读取文件时，将stdin换为 fp,即标准输入缓冲区->文件指针
//     *  fputs(buf,fp) fputs(buf,stdout)
//     */
//    char str[10]={0};
//    fseek(fp,-sizeof(int),SEEK_CUR);
//    while (fgets(str,sizeof (str),fp) != NULL) {
        printf("str = |%s\n",str);
//        fputs(str,stdout);
//    }
//    printf("\n%d\n", strlen(str));

    fclose(fp);

    return 0;
}

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