int main(void)
{
char *str;
/* allocate memory for string */
str = malloc(10);
/* copy "Hello" to string */
strcpy(str, "Hello");
/* display string */
printf("String is %s\n", str);
/* free memory */
free(str);
return 0;
}
函数名: freemem
功 能: 释放先前分配的DOS内存块
用 法: int freemem(unsigned seg);
程序例:
#include
#include
int main(void)
{
unsigned int size, segp;
int stat;
size = 64; /* (64 x 16) = 1024 bytes */
stat = allocmem(size, &segp);
if (stat < 0)
printf("Allocated memory at segment:\
%x\n", segp);
else
printf("Failed: maximum number of\
paragraphs available is %u\n",
stat);
freemem(segp);
return 0;
}
函数名: freopen
功 能: 替换一个流
用 法: FILE *freopen(char *filename, char *type, FILE *stream);
程序例:
#include
int main(void)
{
/* redirect standard output to a file */
if (freopen("OUTPUT.FIL", "w", stdout)
== NULL)
fprintf(stderr, "error redirecting\
stdout\n");
/* this output will go to a file */
printf("This will go into a file.");
/* close the standard output stream */
fclose(stdout);
return 0;
}
函数名: frexp
功 能: 把一个双精度数分解为尾数的指数
用 法: double frexp(double value, int *eptr);
程序例:
#include
#include
int main(void)
{
double mantissa, number;
int exponent;
number = 8.0;
mantissa = frexp(number, &exponent);
printf("The number %lf is ", number);
printf("%lf times two to the ", mantissa);
printf("power of %d\n", exponent);
return 0;
}
函数名: fscanf
功 能: 从一个流中执行格式化输入
用 法: int fscanf(FILE *stream, char *format[,argument...]);
程序例:
#include
#include
int main(void)
{
int i;
printf("Input an integer: ");
/* read an integer from the
standard input stream */
if (fscanf(stdin, "%d", &i))
printf("The integer read was: %i\n",
i);
else
{
fprintf(stderr, "Error reading an \
integer from stdin.\n");
exit(1);
}
return 0;
}
函数名: fseek
功 能: 重定位流上的文件指针
用 法: int fseek(FILE *stream, long offset, int fromwhere);
程序例:
#include
long filesize(FILE *stream);
int main(void)
{
FILE *stream;
stream = fopen("MYFILE.TXT", "w+");
fprintf(stream, "This is a test");
printf("Filesize of MYFILE.TXT is %ld bytes\n", filesize(stream));
fclose(stream);
return 0;
}
long filesize(FILE *stream)
{
long curpos, length;
curpos = ftell(stream);
fseek(stream, 0L, SEEK_END);
length = ftell(stream);
fseek(stream, curpos, SEEK_SET);
return length;
}
函数名: fsetpos
功 能: 定位流上的文件指针
用 法: int fsetpos(FILE *stream, const fpos_t *pos);
程序例:
#include
#include
void showpos(FILE *stream);
int main(void)
{
FILE *stream;
fpos_t filepos;
/* open a file for update */
stream = fopen("DUMMY.FIL", "w+");
/* save the file pointer position */
fgetpos(stream, &filepos);
/* write some data to the file */
f