Welcome to OGeek Q&A Community for programmer and developer-Open, Learning and Share
Welcome To Ask or Share your Answers For Others

Categories

0 votes
1.1k views
in Technique[技术] by (71.8m points)

string formatting - The simplest way of printing a portion of a char[] in C

Let's say I have a char* str = "0123456789" and I want to cut the first and the last three letters and print just the middle, what is the simplest, and safest, way of doing it?

Now the trick: The portion to cut and the portion to print are of variable size, so I could have a very long char*, or a very small one.

See Question&Answers more detail:os

与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…
Welcome To Ask or Share your Answers For Others

1 Reply

0 votes
by (71.8m points)

You can use printf(), and a special format string:

char *str = "0123456789";
printf("%.6s
", str + 1);

The precision in the %s conversion specifier specifies the maximum number of characters to print. You can use a variable to specify the precision at runtime as well:

int length = 6;
char *str = "0123456789";    
printf("%.*s
", length, str + 1);

In this example, the * is used to indicate that the next argument (length) will contain the precision for the %s conversion, the corresponding argument must be an int.

Pointer arithmetic can be used to specify the starting position as I did above.

[EDIT]

One more point, if your string is shorter than your precision specifier, less characters will be printed, for example:

int length = 10;
char *str = "0123456789";
printf("%.*s
", length, str + 5);

Will print "56789". If you always want to print a certain number of characters, specify both a minimum field width and a precision:

printf("%10.10s
", str + 5);

or

printf("%*.*s
", length, length, str + 5);

which will print:

"     56789"

You can use the minus sign to left-justify the output in the field:

printf("%-10.10s
", str + 5);

Finally, the minimum field width and the precision can be different, i.e.

printf("%8.5s
", str);

will print at most 5 characters right-justified in an 8 character field.


与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…
OGeek|极客中国-欢迎来到极客的世界,一个免费开放的程序员编程交流平台!开放,进步,分享!让技术改变生活,让极客改变未来! Welcome to OGeek Q&A Community for programmer and developer-Open, Learning and Share
Click Here to Ask a Question

...