C语言函数大全--f开头的函数（上）

#include <stdio.h>
#include <math.h>

int main(void)
{
    double result, x = -4.5;
    result = fabs(x); // 取绝对值

    float resultf, xf = -3.5;
    resultf = fabsf(xf);

    long double resultL, xL = -2.5;
    resultL = fabsl(xL);

    printf("The absolute value of %lf is %lf\n", x, result);

    printf("The absolute value of %f is %f\n", xf,  resultf);

    printf("The absolute value of %Lf is %Lf\n", xL, resultL);

    return 0;
}

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

int main(void)
{
    FILE *fp;
    char buf[30] = "Hello, Huazie 123456789";
    fp = fopen("temp.txt", "w");
    printf("temp.txt is created and opened\n");
    fwrite(&buf, strlen(buf), 1, fp);
    printf("temp.txt is writed\n");
    fclose(fp);
    printf("temp.txt is closed");
    return 0;
}

#include <stdio.h>

#define fcloseall() _fcloseall();

int main()
{
    int streams_closed;

    fopen("temp.one", "w");
    fopen("temp.two", "w");

    // 关闭打开流
    streams_closed = fcloseall();

    if (streams_closed == EOF)
        perror("Error");
    else
        printf("%d streams were closed.\n", streams_closed);

    return 0;
}

#include <stdlib.h>
#include <stdio.h>
#include <conio.h>

int main()
{
    char *string;
    double value;
    int decpt, sign;

    int ndigit = 10;
    value = 9.876;
    string = fcvt(value, ndigit, &decpt, &sign);
    printf("string = %-18s decpt = %d sign = %d value = %lf\n", string, decpt, sign, value);

    value = -123.45;
    ndigit= 15;
    string = fcvt(value, ndigit, &decpt, &sign);
    printf("string = %-18s decpt = %d sign = %d value = %lf\n", string, decpt, sign, value);

    value = 0.6789e5; /* 科学记数法 scientific notation */
    ndigit = 5;
    string = fcvt(value, ndigit, &decpt, &sign);
    printf("string = %-18s decpt = %d sign = %d value = %lf\n", string, decpt, sign, value);

    return 0;
}

#include <stdio.h>  
#include <math.h>
  
int main() {  

  double x = 5.000011;
    double y = 3.000041;

    double result_d = fdim(x, y);

    float xf = 5.000011f;
    float yf = 3.000031f;
    float result_f = fdimf(xf, yf);

    long double xLD = 5.000011L;
    long double yLD = 3.000021L;
    long double result_ld = fdiml(xLD, yLD);

    printf("fdim(%.6lf, %.6lf) = %.6lf\n", x, y, result_d);
    printf("fdimf(%.6f, %.6f) = %.6f\n", xf, yf, result_f);
    printf("fdiml(%.6Lf, %Lf) = %.6Lf\n", xLD, yLD, result_ld);
  
    return 0;  
}

#include <sys\stat.h>
#include <stdio.h>
#include <fcntl.h>
#include <io.h>

int main(void)
{
    int handle;
    FILE *stream;
    // 打开 temp.txt 文件
    handle = open("temp.txt", O_CREAT | O_RDWR, S_IREAD | S_IWRITE);
    // 将文件描述符和文件流关联
    stream = fdopen(handle, "w");

    if (stream == NULL)
        printf("fdopen failed\n");
    else
    {
        fprintf(stream, "%s:%d\n", "Hello world", 123);
        fclose(stream);
    }
    return 0;
}

#include <stdio.h>

int main(void)
{
    FILE *stream;
    // 以读取模式，打开文件 temp.txt
    stream = fopen("temp.txt", "r");

    // 检查是否文件结束【0：未结束 非0：结束】
    while (!feof(stream))
        printf("%c", fgetc(stream));

    fclose(stream);
    return 0;
}

#include <stdio.h>

int main(void)
{
    FILE *stream;
    // 以写模式打开文件STU.FIL
    stream = fopen("STU.FIL", "w");
    // 通过尝试读取来强制出现错误条件
    (void) getc(stream);
    // 检测流上的错误【返回0，表示未出错；返回非零值，表示出错。】
    if (ferror(stream))
    {
        printf("Error reading from STU.FIL\n");
        // 重置错误和EOF标志
        clearerr(stream);
    }
    fclose(stream);
    return 0;
}

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

void flush(FILE *stream);

int main(void)
{
    FILE *stream;
    char msg[] = "This is a test";

    stream = fopen("STU.FIL", "w");
    fwrite(msg, strlen(msg), 1, stream);

    printf("Press any key to flush STU.FIL:");
    getchar();

    // 将数据刷新到 STU.FIL 中而不关闭它
    flush(stream);

    printf("\nFile was flushed, Press any key to quit:");
    getchar();
    return 0;
}

void flush(FILE *stream)
{
    int duphandle;

    // flush the stream's internal buffer
    fflush(stream);

    // make a duplicate file handle
    duphandle = dup(fileno(stream));

    // close the duplicate handle to flush the DOS buffer
    close(duphandle);
}

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

int main(void)
{
    FILE *stream;
    char string[] = "This is a test";
    char ch;

    stream = fopen("STU.FIL", "w+");
    fwrite(string, strlen(string), 1, stream);
    fseek(stream, 0, SEEK_SET);
    
    do
    {
        ch = fgetc(stream);
        putchar(ch);
    } while (ch != EOF);

    fclose(stream);
    return 0;
}

#include <stdio.h>

int main(void)
{
    char ch;
    printf("Enter a character followed by <Enter>: ");
    // read the character from stdin
    ch = fgetchar();
    printf("The character read is: '%c'\n", ch);
    return 0;
}

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

int main(void)
{
    FILE *stream;
    char string[] = "This is a test";
    fpos_t filepos;
    stream = fopen("STU.FIL", "w+");
    fwrite(string, strlen(string), 1, stream);
    // report the file pointer position
    fgetpos(stream, &filepos);
    printf("The file pointer is at byte %lld\n", filepos);
    fclose(stream);
    return 0;
}

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

int main(void)
{
    FILE *stream;
    char str[] = "This is a test\n12344";
    char msg[20];

    stream = fopen("STU.FIL", "w+");
    fwrite(str, strlen(str), 1, stream);
    // seek to the start of the file
    fseek(stream, 0, SEEK_SET);
    while(!feof(stream))
    {
        fgets(msg, strlen(str) + 1, stream);
        printf("%s", msg);
    }
    fclose(stream);
    return 0;
}

#include <stdio.h>
#include <fcntl.h>
#include <io.h>

int main(void)
{
    int handle;
    char buf[30] = "This is a test\n12344";
    handle = open("STU.FIL", O_CREAT);
    write(handle, buf, strlen(buf));
    printf("file length in bytes: %ld\n", filelength(handle));
    close(handle);
    return 0;
}

#include <stdio.h>
#include <fcntl.h>
#include <io.h>

int main(void)
{
    FILE *stream;
    char buf[30] = "This is a test\n12344";
    stream = fopen("STU.FIL", "w+");
    fwrite(buf, strlen(buf), 1, stream);
    // 清除读写缓冲区，并将缓冲区内的数据写回参数stream指向的文件中。
    fflush(stream);
    // 获取参数stream指定的文件流所使用的文件描述符
    int handle = fileno(stream);
    printf("file length in bytes: %ld\n", filelength(handle));
    fclose(stream);
    return 0;
}

#include <graphics.h>

int main(void)
{
    int gdriver = DETECT, gmode;
    int xcenter, ycenter, i;

    initgraph(&gdriver,&gmode,"");
    xcenter = getmaxx() / 2;
    ycenter = getmaxy() / 2;

    for (i=EMPTY_FILL; i<USER_FILL; i++)
    {
        cleardevice();
        // 设置填充图样和颜色
        setfillstyle(i, WHITE);
        fillellipse(xcenter, ycenter, 100, 50);
        getch();
    }

    closegraph();
    return 0;
}

#include <graphics.h>
#include <stdlib.h>
#include <stdio.h>

int main(void)
{
    int gdriver = DETECT, gmode, errorcode;
    int i, maxx, maxy;

    int poly[8];

    initgraph(&gdriver, &gmode, "");

    errorcode = graphresult();
    if (errorcode != grOk)
    {
        printf("Graphics error: %s\n", grapherrormsg(errorcode));
        printf("Press any key to halt:");
        getch();
        exit(1);
    }

    maxx = getmaxx();
    maxy = getmaxy();

    poly[0] = 20;
    poly[1] = maxy / 2;

    poly[2] = maxx - 20;
    poly[3] = 20;

    poly[4] = maxx - 50;
    poly[5] = maxy - 20;

    poly[6] = maxx / 2;
    poly[7] = maxy / 2;

    for (i=EMPTY_FILL; i<USER_FILL; i++)
    {
        setfillstyle(i, getmaxcolor());
        fillpoly(4, poly);
        getch();
    }

    closegraph();
    return 0;
}

#include<stdio.h>
#include<io.h>

int main()
{
    int handle;
    struct _finddata_t FileInfo;
    // 搜索与指定的文件名称匹配的第一个文件，若成功则返回第一个文件的文件描述符，否则返回-1L。
    if((handle=_findfirst("E:\\Pic\\*.png", &FileInfo))==-1L)
        printf("没有找到匹配的项目\n");
    else
    {
        printf("handle=%d\n", handle);
        printf("%s\n\n", FileInfo.name);
        // 搜索与_findfirst函数提供的文件名称匹配的下一个实例，若成功则返回0，否则返回－1
        while(_findnext(handle, &FileInfo)==0)
            printf("%s\n",FileInfo.name);
        _findclose(handle);
    }
    return 0;
}

#include<stdio.h>
#include<math.h>

int main()
{
    double x = NAN, y = INFINITY, z = 10.24;
    printf("finite(%.2lf) = %d\n", x, finite(x));
    printf("finite(%.2lf) = %d\n", y, finite(y));
    printf("finite(%.2lf) = %d\n", z, finite(z));

    float xf = NAN, yf = INFINITY, zf = 5.63;
    printf("\nfinitef(%.2f) = %d\n", xf, finitef(xf));
    printf("finitef(%.2f) = %d\n", yf, finitef(yf));
    printf("finitef(%.2f) = %d\n", zf, finitef(zf));
    return 0;
}

#include <graphics.h>
#include <stdlib.h>
#include <stdio.h>

int main(void)
{
    int gdriver = DETECT, gmode, errorcode;
    int maxx, maxy;

    initgraph(&gdriver, &gmode, "");

    errorcode = graphresult();
    if (errorcode != grOk)
    {
      printf("Graphics error: %s\n", grapherrormsg(errorcode));
      printf("Press any key to halt:");
      getch();
      exit(1);
    }

    maxx = getmaxx();
    maxy = getmaxy();

    // select drawing color
    setcolor(getmaxcolor());
    // select fill color
    setfillstyle(SOLID_FILL, getmaxcolor());
    // draw a border around the screen
    rectangle(0, 0, maxx, maxy);
    // draw some circles
    circle(maxx / 3, maxy /2, 50);
    circle(maxx / 2, 20, 100);
    circle(maxx-20, maxy-50, 75);
    circle(20, maxy-20, 25);

    getch();

    // fill in bounded region
    floodfill(2, 2, getmaxcolor());

    getch();
    closegraph();
    return 0;
}