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setvbuf
语法: #include <stdio.h> int setvbuf( FILE *stream, char *buffer, int mode, size_t size );
int setvbuf(
FILE *stream,
char *buffer,
int mode,
size_t size
);
Parameters
stream
Pointer to FILE structure.
buffer
User-allocated buffer.
mode
Mode of buffering.
size
Buffer size in bytes. Allowable range: 2 <= size <= INT_MAX (2147483647). Internally, the value supplied for size is rounded down to the nearest multiple of 2.
函数setvbuf()设置用于stream(流)的缓冲区到buffer(缓冲区),其大小为size(大小). mode(方式)可以是:
_IOFBF, 表示完全缓冲
_IOLBF, 表示线缓冲
_IONBF, 表示无缓存
程序例:
#include <stdio.h>
int main(void)
{
FILE *input, *output;
char bufr[512];
input = fopen("file.in", "r+b");
output = fopen("file.out", "w");
/* set up input stream for minimal disk access,
using our own character buffer */
if (setvbuf(input, bufr, _IOFBF, 512) != 0)
printf("failed to set up buffer for input file\n");
else
printf("buffer set up for input file\n");
/* set up output stream for line buffering using space that
will be obtained through an indirect call to malloc */
if (setvbuf(output, NULL, _IOLBF, 132) != 0)
printf("failed to set up buffer for output file\n");
else
printf("buffer set up for output file\n");
/* perform file I/O here */
/* close files */
fclose(input);
fclose(output);
return 0;
}
/* setvbuf example */
#include <stdio.h>
int main ()
{
FILE *pFile;
pFile=fopen ("myfile.txt","w");
setvbuf ( pFile , NULL , _IOFBF , 1024 );
// File operations here
fclose (pFile);
return 0;
}
在这个例子中，每次写1024字节，所以只有缓冲区满了（有1024字节），才往文件写入数据，可以减少IO次数
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