How to format strings using printf() to get equal length in the output

Solution 1:

You can specify a width on string fields, e.g.

printf("%-20s", "initialization...");

And then whatever's printed with that field will be blank-padded to the width you indicate.

The - left-justifies your text in that field.

Solution 2:

printf allows formatting with width specifiers. For example,

printf( "%-30s %s\n", "Starting initialization...", "Ok." );

You would use a negative width specifier to indicate left-justification because the default is to use right-justification.

Solution 3:

Additionally, if you want the flexibility of choosing the width, you can choose between one of the following two formats (with or without truncation):

int width = 30;
// No truncation uses %-*s
printf( "%-*s %s\n", width, "Starting initialization...", "Ok." );
// Output is "Starting initialization...     Ok."

// Truncated to the specified width uses %-.*s
printf( "%-.*s %s\n", width, "Starting initialization...", "Ok." );
// Output is "Starting initialization... Ok."

Solution 4:

There's also the %n modifier which can help in certain circumstances. It returns the column on which the string was so far. Example: you want to write several rows that are within the width of the first row like a table.

int width1, width2;
int values[6][2];
printf("|%s%n|%s%n|\n", header1, &width1, header2, &width2);

for(i=0; i<6; i++)
   printf("|%*d|%*d|\n", width1, values[i][0], width2, values[i][1]);

will print two columns of the same width of whatever length the two strings header1 and header2 may have. I don't know if all implementations have the %n, but Solaris and Linux do.