Atof(), atoi(), atol() functions [detailed]

Introduction to this issue
This paper mainly introduces ：atof()、atoi()、atol() How functions are used , What are the functions , And some noteworthy points in use .

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One 、 Preface

   C Language provides some library functions that can convert numeric strings into numbers , for example atof()、atoi()、atol() function . The functions of these functions are introduced below ：

1. atof() function ： Converts a string to double Type data .
2. atoi() function ： Converts a string to int Type data .
3. atol() function ： Replace the string with long int Type data .

   Be careful ： If the input cannot be converted to this type of data , The return value is 0.

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Two 、atof() function

double atof( const char *string );

   stay VS In the compiler atof() The library function needs to reference two header files before calling <stdlib.h> and <math.h>.atof() The function needs to pass a string as a parameter , And the string needs to have a certain format ：

1. Scientific form of counting ：[ Space ][+/-][ Numbers ][. Numbers ][ {d |D |e |E }[+/-] Numbers ]
2. Decimal form ：[ Space ][+/-][ Numbers ][. Numbers ]

  atof() The parameter string is scanned , Skip the preceding space character , It's not until you meet a number or a sign that you start to convert , Then judge strictly according to the format requirements , Until the format is illegal or the end of string flag is encountered ‘\0’ Will end the conversion , Return to one double Data of type . Take a few examples ：

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3、 ... and 、atoi()、atol() function

int atoi( const char *string );
long atol( const char *string );

   stay VS In the compiler atoi() and atol() Function needs to reference a header file <stdlib.h>. There is no difference between these two functions in the parameter transfer part , There are only differences in the return value of the function ：atoi() Back to a int Type data ,atol() Back to a long int Type data .
   The string of parameters also has a certain format ：[ Space ][+/-][ Numbers ]. and atoi()、atol() The function will scan the parameter string first , Skip the preceding space character , It's not until you meet a number or a sign that you start to convert , Then until you encounter non numeric characters or string end flags ‘\0’ Will end the conversion , Returns a number . Take a few examples ：

   Be careful ： If atof() function 、atio() function 、atol() Overflow occurs when the return value of a function is greater than the maximum value of its return type , As a result, some part of the returned data is lost .