C语言库函数大全及应用实例十

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int sort_function( const void *a, const void *b);

char list[5][4] = { "cat", "car", "cab", "cap", "can" };

int main(void)
{
int x;

qsort((void *)list, 5, sizeof(list[0]), sort_function);
for (x = 0; x < 5; x++)
printf("%s\n", list[x]);
return 0;
}

int sort_function( const void *a, const void *b)
{
return( strcmp(a,b) );
}

函数名: qsort
功 能: 使用快速排序例程进行排序
用 法: void qsort(void *base, int nelem, int width, int (*fcmp)());
程序例:

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int sort_function( const void *a, const void *b);

char list[5][4] = { "cat", "car", "cab", "cap", "can" };

int main(void)
{
int x;

qsort((void *)list, 5, sizeof(list[0]), sort_function);
for (x = 0; x < 5; x++)
printf("%s\n", list[x]);
return 0;
}

int sort_function( const void *a, const void *b)
{
return( strcmp(a,b) );
}

函数名: raise
功 能: 向正在执行的程序发送一个信号
用 法: int raise(int sig);
程序例:

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int main(void)
{
int a, b;

a = 10;
b = 0;
if (b == 0)
/* preempt divide by zero error */
raise(SIGFPE);
a = a / b;
return 0;
}

函数名: rand
功 能: 随机数发生器
用 法: void rand(void);
程序例:

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int main(void)
{
int i;

printf("Ten random numbers from 0 to 99\n\n");
for(i=0; i<10; i++)
printf("%d\n", rand() % 100);
return 0;
}

函数名: randbrd
功 能: 随机块读
用 法: int randbrd(struct fcb *fcbptr, int reccnt);
程序例:

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int main(void)
{
char far *save_dta;
char line[80], buffer[256];
struct fcb blk;
int i, result;

/* get user input file name for dta */
printf("Enter drive and file name (no path - i.e. a:file.dat)\n");
gets(line);

/* put file name in fcb */
if (!parsfnm(line, &blk, 1))
{
printf("Error in call to parsfnm\n");
exit(1);
}
printf("Drive #%d file: %s\n\n", blk.fcb_drive, blk.fcb_name);

/* open file with DOS FCB open file */
bdosptr(0x0F, &blk, 0);

/* save old dta, and set new one */
save_dta = getdta();
setdta(buffer);

/* set up info for the new dta */
blk.fcb_recsize = 128;
blk.fcb_random = 0L;
result = randbrd(&blk, 1);

/* check results from randbrd */
if (!result)
printf("Read OK\n\n");
else
{
perror("Error during read");
exit(1);
}

/* read in data from the new dta */
printf("The first 128 characters are:\n");
for (i=0; i<128; i++)
putchar(buffer[i]);

/* restore previous dta */
setdta(save_dta);

return 0;
}

函数名: randbwr
功 能: 随机块写
用 法: int randbwr(struct fcp *fcbptr, int reccnt);
程序例:

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int main(void)
{
char far *save_dta;
char line[80];
char buffer[256] = "RANDBWR test!";
struct fcb blk;
int result;

/* get new file name from user */
printf("Enter a file name to create (no path - ie. a:file.dat\n");
gets(line);

/* parse the new file name to the dta */
parsfnm(line,&blk,1);
printf("Drive #%d file: %s\n", blk.fcb_drive, blk.fcb_name);

/* request DOS services to create file */
if (bdosptr(0x16, &blk, 0) == -1)
{
perror("Error creating file");
exit(1);
}

/* save old dta and set new dta */
save_dta = getdta();
setdta(buffer);

/* write new records */
blk.fcb_recsize = 256;
blk.fcb_random = 0L;
result = randbwr(&blk, 1);

if (!result)
printf("Write OK\n");
else
{
perror("Disk error");
exit(1);
}

/* request DOS services to close the file */
if (bdosptr(0x10, &blk, 0) == -1)
{
perror("Error closing file");
exit(1);
}

/* reset the old dta */
setdta(save_dta);

return 0;
}

函数名: random
功 能: 随机数发生器
用 法: int random(int num);
程序例:

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/* prints a random number in the range 0 to 99 */
int main(void)
{
randomize();
printf("Random number in the 0-99 range: %d\n", random (100));
return 0;
}

函数名: randomize
功 能: 初始化随机数发生器
用 法: void randomize(void);
程序例:

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int main(void)
{
int i;

randomize();
printf("Ten random numbers from 0 to 99\n\n");
for(i=0; i<10; i++)
printf("%d\n", rand() % 100);
return 0;
}

函数名: read
功 能: 从文件中读
用 法: int read(int handle, void *buf, int nbyte);
程序例:

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int main(void)
{
void *buf;
int handle, bytes;

buf = malloc(10);

/*
Looks for a file in the current directory named TEST.$$$ and attempts
to read 10 bytes from it. To use this example you should create the
file TEST.$$$
*/
if ((handle =
open("TEST.$$$", O_RDONLY | O_BINARY, S_IWRITE | S_IREAD)) == -1)
{
printf("Error Opening File\n");
exit(1);
}

if ((bytes = read(handle, buf, 10)) == -1) {
printf("Read Failed.\n");
exit(1);
}
else {
printf("Read: %d bytes read.\n", bytes);
}
return 0;
}

函数名: realloc
功 能: 重新分配主存
用 法: void *realloc(void *ptr, unsigned newsize);
程序例:

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int main(void)
{
char *str;

/* allocate memory for string */
str = malloc(10);

/* copy "Hello" into string */
strcpy(str, "Hello");

printf("String is %s\n Address is %p\n", str, str);
str = realloc(str, 20);
printf("String is %s\n New address is %p\n", str, str);

/* free memory */
free(str);

return 0;
}

函数名: rectangle
功 能: 画一个矩形
用 法: void far rectangle(int left, int top, int right, int bottom);
程序例:

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int main(void)
{
/* request auto detection */
int gdriver = DETECT, gmode, errorcode;
int left, top, right, bottom;

/* initialize graphics and local variables */
initgraph(&gdriver, &gmode, "");

/* read result of initialization */
errorcode = graphresult();
if (errorcode != grOk) /* an error occurred */
{
printf("Graphics error: %s\n", grapherrormsg(errorcode));
printf("Press any key to halt:");
getch();
exit(1); /* terminate with an error code */
}

left = getmaxx() / 2 - 50;
top = getmaxy() / 2 - 50;
right = getmaxx() / 2 + 50;
bottom = getmaxy() / 2 + 50;

/* draw a rectangle */
rectangle(left,top,right,bottom);

/* clean up */
getch();
closegraph();
return 0;
}

函数名: registerbgidriver
功 能: 登录已连接进来的图形驱动程序代码
用 法: int registerbgidriver(void(*driver)(void));
程序例:

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int main(void)
{
/* request auto detection */
int gdriver = DETECT, gmode, errorcode;

/* register a driver that was added into graphics.lib */
errorcode = registerbgidriver(EGAVGA_driver);

/* report any registration errors */
if (errorcode < 0)
{
printf("Graphics error: %s\n", grapherrormsg(errorcode));
printf("Press any key to halt:");
getch();
exit(1); /* terminate with an error code */
}

/* initialize graphics and local variables */
initgraph(&gdriver, &gmode, "");

/* read result of initialization */
errorcode = graphresult();
if (errorcode != grOk) /* an error occurred */
{
printf("Graphics error: %s\n", grapherrormsg(errorcode));
printf("Press any key to halt:");
getch();
exit(1); /* terminate with an error code */
}

/* draw a line */
line(0, 0, getmaxx(), getmaxy());

/* clean up */
getch();
closegraph();
return 0;
}

函数名: remove
功 能: 删除一个文件
用 法: int remove(char *filename);
程序例:

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int main(void)
{
char file[80];

/* prompt for file name to delete */
printf("File to delete: ");
gets(file);

/* delete the file */
if (remove(file) == 0)
printf("Removed %s.\n",file);
else
perror("remove");

return 0;
}

函数名: rename
功 能: 重命名文件
用 法: int rename(char *oldname, char *newname);
程序例:

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int main(void)
{
char oldname[80], newname[80];

/* prompt for file to rename and new name */
printf("File to rename: ");
gets(oldname);
printf("New name: ");
gets(newname);

/* Rename the file */
if (rename(oldname, newname) == 0)
printf("Renamed %s to %s.\n", oldname, newname);
else
perror("rename");

return 0;
}

函数名: restorecrtmode
功 能: 将屏幕模式恢复为先前的imitgraph设置
用 法: void far restorecrtmode(void);
程序例:

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int main(void)
{
/* request auto detection */
int gdriver = DETECT, gmode, errorcode;
int x, y;

/* initialize graphics and local variables */
initgraph(&gdriver, &gmode, "");

/* read result of initialization */
errorcode = graphresult();
if (errorcode != grOk) /* an error occurred */
{
printf("Graphics error: %s\n", grapherrormsg(errorcode));
printf("Press any key to halt:");
getch();
exit(1); /* terminate with an error code */
}

x = getmaxx() / 2;
y = getmaxy() / 2;

/* output a message */
settextjustify(CENTER_TEXT, CENTER_TEXT);
outtextxy(x, y, "Press any key to exit graphics:");
getch();

/* restore system to text mode */
restorecrtmode();
printf("We‘re now in text mode.\n");
printf("Press any key to return to graphics mode:");
getch();

/* return to graphics mode */
setgraphmode(getgraphmode());

/* output a message */
settextjustify(CENTER_TEXT, CENTER_TEXT);
outtextxy(x, y, "We‘re back in graphics mode.");
outtextxy(x, y+textheight("W"), "Press any key to halt:");

/* clean up */
getch();
closegraph();
return 0;
}

函数名: rewind
功 能: 将文件指针重新指向一个流的开头
用 法: int rewind(FILE *stream);
程序例:

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int main(void)
{
FILE *fp;
char *fname = "TXXXXXX", *newname, first;

newname = mktemp(fname);
fp = fopen(newname,"w+");
fprintf(fp,"abcdefghijklmnopqrstuvwxyz");
rewind(fp);
fscanf(fp,"%c",&first);
printf("The first character is: %c\n",first);
fclose(fp);
remove(newname);

return 0;
}

函数名: rmdir
功 能: 删除DOS文件目录
用 法: int rmdir(char *stream);
程序例:

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#define DIRNAME "testdir.$$$"

int main(void)
{
int stat;

stat = mkdir(DIRNAME);
if (!stat)
printf("Directory created\n");
else
{
printf("Unable to create directory\n");
exit(1);
}

getch();
system("dir/p");
getch();

stat = rmdir(DIRNAME);
if (!stat)
printf("\nDirectory deleted\n");
else
{
perror("\nUnable to delete directory\n");
exit(1);
}

return 0;
}