printf gets fgets辨析

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#character #newline #stream #file #string #input

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本文介绍了C语言中处理字符串的方法，包括使用scanf、fgets、gets等函数的区别，特别强调了安全性和空格处理的重要性，并提供了一个去除字符串中空格的具体实现案例。

一、辨析

（1）scanf不能读包含有空格的字符串。

（2）gets和fgets皆读一行内容，可含空格，gets不安全，尽量用fgets。

（3）注意：若gets和fgets前有输入（如scanf），则要使用getchar（）后再使用gets或fgets，防止将前面的空格读入。

二、facts/关键

（1）明确各个函数对空格（ ‘ ’）的处理。

（2）想象有个指针指向终端或文件，依次后移。

三、代码

输入：长度<30的字符串，可包含空格

输出：去掉空格后的字符串

#include<stdio.h>

#include<stdlib.h>

#define MAX_CHAR_NUM 30

void cut_string(char * p1,char * p2)

{

int i=0;

int j=0;

while(p1[i]!='/0')

{

if (p1[i]!=' ')

{

p2[j]=p1[i];

j++;

}

i++;

}

p2[j]='/0';

}

int main()

{

char a1[MAX_CHAR_NUM];

char a2[MAX_CHAR_NUM]; // (1)allocate memory(data struct)

printf("please input the string:/n");

fgets(a1,MAX_CHAR_NUM+1,stdin); // (2)initialize original data

cut_string(a1,a2); // (3)operate

printf("%s/n",a2); // (4)print result

}

#if 0 //test_code,incomplete

int main()

{

int num_char;

char *p1;

char *p2;

scanf("%d",&num_char);

printf("num_char is:%d/n",num_char);

p1=(char*)malloc(sizeof(char)*(num_char+1));

p2=(char*)malloc(sizeof(char)*(num_char+1));

getchar();

fgets(p1,num_char+1,stdin);

printf("%s/n",p1);

cut_string2(num_char,p1,p2);

printf("%s",p2);

}

#endif

另转

http://linux.about.com/library/cmd/blcmdl3_fgets.htm

NAME

fgetc, fgets, getc, getchar, gets, ungetc - input of characters and strings

SYNOPSIS

#include <stdio.h
>


int fgetc(FILE *
stream
);

char *fgets(char *
s
, int 
size
, FILE *
stream
);

int getc(FILE *
stream
);

int getchar(void);

char *gets(char *
s
);

int ungetc(int 
c
, FILE *
stream
);

DESCRIPTION

fgetc() reads the next character from stream and returns it as an unsigned char cast to an int , or EOF on end of file or error.

getc() is equivalent to fgetc() except that it may be implemented as a macro which evaluatesstream more than once.

getchar() is equivalent to getc( stdin ) .

gets() reads a line from stdin into the buffer pointed to by s until either a terminating newline or EOF , which it replaces with '/0' . No check for buffer overrun is performed (see BUGS below).

fgets() reads in at most one less than size characters from stream and stores them into the buffer pointed to by s . Reading stops after an EOF or a newline. If a newline is read, it is stored into the buffer. A '/0' is stored after the last character in the buffer.

ungetc() pushes c back to stream , cast to unsigned char , where it is available for subsequent read operations. Pushed - back characters will be returned in reverse order; only one pushback is guaranteed.

Calls to the functions described here can be mixed with each other and with calls to other input functions from the stdio library for the same input stream.

For non-locking counterparts, see unlocked_stdio (3).