fgets
char *fgets(char *str, int num, FILE *stream);
1. Get string from stream
        Reads characters from stream and stores them as a C string into str until (num-1) characters have been read or either a newline or the end-of-file is reached, whichever happens first.
        A newline character makes fgets stop reading, but it is considered a valid character by the function and included in the string copied to str.
        A terminating null character is automatically appended after the characters copied to str.
        Notice that fgets is quite different from gets: not only fgets accepts a stream argument, but also allows to specify the maximum size of str and includes in the string any ending newline character.
1.1 Parameters
str
        Pointer to an array of chars where the string read is copied.
num
        Maximum number of characters to be copied into str (including the terminating null-character).
stream
        Pointer to a FILE object that identifies an input stream.
        stdin can be used as argument to read from the standard input.
1.2 Return Value
        On success, the function returns str.
        If the end-of-file is encountered while attempting to read a character, the eof indicator is set (feof). If this happens before any characters could be read, the pointer returned is a null pointer (and the contents of str remain unchanged).
        If a read error occurs, the error indicator (ferror) is set and a null pointer is also returned (but the contents pointed by str may have changed).
2. Example
2.1 example
/*
 ============================================================================
 Name        : fgets_example_1.c
 Author      : foreverstrong
 Version     :
 Copyright   : Your copyright notice
 Description : Hello World in C, Ansi-style
 ============================================================================
 */

/* fgets example */
#include <stdio.h>

int main()
{
	FILE *pFile;
	char mystring[100];

	pFile = fopen("myfile.txt", "r");
	if (pFile == NULL)
	{
		perror("Error opening file");
	}
	else
	{
		if (fgets(mystring, 100, pFile) != NULL)
		{
			puts(mystring);
		}
		fclose(pFile);
	}
	return 0;
}
        This example reads the first line of myfile.txt or the first 99 characters, whichever comes first, and prints them on the screen.
2.2 myfile.txt


Output:
$forever strong$
3. fgets
        Defined in header <stdio.h>
char *fgets( char          *str, int count, FILE          *stream ); (until C99)
char *fgets( char *restrict str, int count, FILE *restrict stream ); (since C99)
char *fgets( char          *str, int count, FILE          *stream ); (C99 前)
char *fgets( char *restrict str, int count, FILE *restrict stream ); (C99 起
        Reads at most count - 1 characters from the given file stream and stores them in the character array pointed to by str. Parsing stops if end-of-file occurs or a newline character is found, in which case str will contain that newline character. If no errors occur, writes a null character at the position immediately after the last character written to str.
        The behavior is undefined if count is less than 1.
3.1 Parameters
       str - pointer to an element of a char array
        count - maximum number of characters to write (typically the length of str)
        stream - file stream to read the data from
3.2 Return value
        str on success, null pointer on failure.
        If the failure has been caused by end-of-file condition, additionally sets the eof indicator (see feof()) on stream. The contents of the array pointed to by str are not altered in this case.
        If the failure has been caused by some other error, sets the error indicator (see ferror()) on stream. The contents of the array pointed to by str are indeterminate (it may not even be null-terminated).
3.3 Notes
        POSIX additionally requires that fgets sets errno if it encounters an failure other than the end-of-file condition.
        Although the standard specification is ambiguous in the case where count==1, common implementations read no characters, store zero in str[0], and report success (return str)
4. Example
4.1 example
/*
 ============================================================================
 Name        : fgets_example_2.c
 Author      : foreverstrong
 Version     :
 Copyright   : Your copyright notice
 Description : Hello World in C, Ansi-style
 ============================================================================
 */

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

int main(void)
{
	FILE* tmpf = tmpfile();
	fputs("Alan Turing\n", tmpf);
	fputs("John von Neumann\n", tmpf);
	fputs("Alonzo Church\n", tmpf);

	rewind(tmpf);

	char buf[8];
	while (fgets(buf, sizeof buf, tmpf) != NULL)
	{
		printf("\"%s\"\n", buf);
	}

	if (feof(tmpf))
	{
		puts("End of file reached");
	}
}
Output:
"Alan Tu"
"ring
"
"John vo"
"n Neuma"
"nn
"
"Alonzo "
"Church
"
End of file reached

References
http://en.cppreference.com/w/c/io/fgets
http://zh.cppreference.com/w/c/io/fgets
http://www.cplusplus.com/reference/cstdio/fgets/

fgets 函数
原型：char *fgets(char *s,int size,FILE *stream);
功能：

从stream指定的文件内读入字符，保存到s所指定的内存空间
参数：

s           字符串

size      指定最大读取字符串的长度（size-1）

stream  文件指针
例子

#include <stdio.h>

int main()

{

char str[100] = {0};

fgets(str, sizeof(str), stdin);

printf(“str = %s\n”, str);

}
**
sprintf 函数
**
原型：

int sprintf(char *str,const char *fomat,…)
功能：

sprintf的作用是将一个格式化的字符串输出到一个目的字符串中
参数：

str :字符串首地址

format：格式化字符串

				/*************************************************
				 *功能：从文件流中读取字符串到s指向的空间
				 *参数： 
				 *			@s      存放读取到的数据的缓存区首地址
				 *			@size   读取size-1,补'\0'
				 *			@stream 文件流指针
				 *返回值：
				 ************************************************/			
				 char *fgets(char *s, int size, FILE *stream);


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

int main(int argc, const char *argv[])
{
	char buf[32] = { 0 };
	char *p = NULL;

    memset(buf, 0, sizeof(buf));
	p = fgets(buf, 5, stdin);
	if(NULL == p)
    {
		perror("fgets");
		return -1;
	}

	printf("buf:%s\n", buf);
	printf("p:%s\n", p);

	return 0;
}



测试结果

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linux fgets 阻塞
www.myexceptions.net  网友分享于：2013-09-23   搜索量：159次
场景：linux下fgets(.stdin)不阻塞？解决方案
linux下fgets(..,..,stdin)不阻塞？？
我编写了一个修改文档的程序，但是不知道为什么用fgets(buf,1024,stdin)的时候就不阻塞，我是分为两个函数写的，两个函数分别工作的时候就正常，两个函数合起来工作的时候就会这样，求救！！
函数如下：
find函数寻找对应项，modify函数修改对应项。
#include    
extern   int   modify(FILE   *fp);
int   main()
{
FILE   *fp;
if(fp=fopen( "./t.txt ", "r+ ")==NULL)
{
printf( "there   is   no   such   file ");
return   -1;
}
find(fp);
modify(fp);
fclose(fp);
return   0;
}
int   find(FILE   *fp)
{
char   *t;
char   *idata;
char   *namebuf,*buf2,*addr,*tempbuf;
char   *searchname;
char   *tsearchname,*tnamebuf;
long   count;
long   offsize;
offsize=0;
fseek(fp,0,SEEK_SET);
searchname=(unsigned   char   *)malloc(1024);
idata=(unsigned   char   *)malloc(1024);
tsearchname=(unsigned   char   *)malloc(1024);
tsearchname=searchname;
while((*searchname=(unsigned   char)fgetc(stdin))!= ': ')
{
searchname++;
}
namebuf=(unsigned   char   *)malloc(1024);
tempbuf=(unsigned   char   *)malloc(1024);
tnamebuf=(unsigned   char   *)malloc(1024);
namebuf=tnamebuf;
while((t=fgets(tempbuf,1024,fp))!=NULL)
{
fseek(fp,offsize,SEEK_SET);
while((*tnamebuf=(unsigned   char)fgetc(fp))!= ': ')
{
tnamebuf++;
printf( "the   number   is:%s\n ",namebuf);
}
printf( "namebuf:%s\nsearchname:%s\n ",namebuf,tsearchname);
int   a=0;
if((a=strcmp(namebuf,tsearchname))==0)
break;
printf( "strcmp   is:%d\n ",a);
tnamebuf=namebuf;
fgets(tempbuf,1024,fp);
offsize=ftell(fp);
printf( "%s\n ",tempbuf);
}
if(t==NULL)
{
printf( "can 't   find   the   number\n ");
return   1;
}
else
{
printf( "the   number   %s   is   found\n ",namebuf);
printf( "end   here\n ");
}
printf( "enter   your   data   **:**\n ");
printf( "yeye\n ");
return   0;
}
int   modify(FILE   *fp)
{
char   *pointbuftemp;
char   *buf,*buf2,*buftemp;
int   rest;
long   current,next,nextnext,departure;
buf=(unsigned   char   *)malloc(1024);
buftemp=(unsigned   char   *)malloc(1024);
buf2=buf;
current=ftell(fp);
rest=1024;
fgets(buf,rest,fp);
next=ftell(fp);
departure=0;
while(fgets(buf,rest,fp)!=NULL)
{
nextnext=ftell(fp);
departure=nextnext-next;
next=ftell(fp);
rest-=departure;
buf+=departure;
}
fseek(fp,current,SEEK_SET);
fgets(buftemp,1024,stdin);
fputs(buftemp,fp);
fputs(buf2,fp);
printf( "fflush?\n ");
return   0;
}
请问这是什么原因，应该怎么办呢？谢谢！！
------解决方案--------------------
设这样的
*searchname=(unsigned char)fgetc(stdin)!= ': '
读完以后,缓冲区里的\n号没读取出来.在modify内再用fgets(buftmp,1024,stdin)读时就会把这个 '\n '读走.
这样改一下就可以了:
while((*searchname=(unsigned char)fgetc(stdin))!= ': ')
{
searchname++;
}
fgetc(stdin);   //添加一句.
不过说实话,楼主的程序有很多地方都是冗余的.
你的malloc分配的空间,好象都没free吧.
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